United States customary units
United States customary units are a system of measurements used in the United States. The United States customary system developed from English units which were in use in the British Empire before the U. S. became an independent country. However, the United Kingdom's system of measures was overhauled in 1824 to create the imperial system, changing the definitions of some units. Therefore, while many U. S. units are similar to their Imperial counterparts, there are significant differences between the systems. The majority of U. S. customary units were redefined in terms of the meter and the kilogram with the Mendenhall Order of 1893 and, in practice, for many years before. These definitions were refined by the international yard and pound agreement of 1959. Americans use customary units in commercial activities, as well as for personal and social use. In science, many sectors of industry, some of government and military, metric units are used; the International System of Units, the modern form of the metric system, is preferred for many uses by the U.
S. National Institute of Standards and Technology. For newer units of measure where there is no traditional customary unit, international units are used, sometimes mixed with customary units, such as electrical resistance of wire expressed in ohms per thousand feet; the United States system of units is similar to the British imperial system. Both systems are derived from English units, a system which had evolved over the millennia before American independence, which had its roots in Roman and Anglo-Saxon units; the customary system was championed by the U. S.-based International Institute for Preserving and Perfecting Weights and Measures in the late 19th century. Advocates of the customary system saw the French metric, system as atheistic. An auxiliary of the Institute in Ohio published a poem with wording such as "down with every'metric' scheme" and "A perfect inch, a perfect pint". One adherent of the customary system called it "a just weight and a just measure, which alone are acceptable to the Lord".
The U. S. government passed the Metric Conversion Act of 1975, which made the metric system "the preferred system of weights and measures for U. S. trade and commerce". The legislation states that the federal government has a responsibility to assist industry as it voluntarily converts to the metric system, i.e. metrification. This is most evident in U. S. labeling requirements on food products, where SI units are always presented alongside customary units. According to the CIA Factbook, the United States is one of three nations that have not adopted the metric system as their official system of weights and measures. U. S. Customary units are used on consumer products and in industrial manufacturing. Metric units are standard in science, medicine, as well as many sectors of industry and government, including the military. There are anecdotal objections to the use of metric units in carpentry and the building trades, on the basis that it is easier to remember an integer number of inches plus a fraction than a measurement in millimeters, or that foot-inch measurements are more suitable when distances are divided into halves and quarters in parallel.
The metric system lacks a parallel to the foot. For measuring length, the U. S. customary system uses the inch, foot and mile, which are the only four customary length measurements in everyday use. Since July 1, 1959, these have been defined on the basis of 1 yard = 0.9144 meters except for some applications in surveying. The U. S. the United Kingdom and other Commonwealth countries agreed on this definition, so it is termed international measure. When international measure was introduced in the English-speaking countries, the basic geodetic datum in North America was the North American Datum of 1927, constructed by triangulation based on the definition of the foot in the Mendenhall Order of 1893, 1 foot = 1200/3937 meters: this definition was retained for data derived from NAD27, but renamed the US survey foot to distinguish it from the international foot. For most applications, the difference between the two definitions is insignificant – one international foot is 0.999998 of a US survey foot, for a difference of about 1/8 inch per mile – but it affects the definition of the State Plane Coordinate Systems, which can stretch over hundreds of miles.
The NAD27 was replaced in the 1980s by the North American Datum of 1983, defined in meters. The SPCSs were updated, but the National Geodetic Survey left the decision of which definition of the foot to use to the individual states. All SPCSs are defined in meters, but seven states have SPCSs defined in US survey feet and an eighth state in international feet: the other 42 states use only meter-based SPCSs. State legislation is important for determining the conversion factor to be used for everyday land surveying and real estate transactions, although the difference is of no practical significance given the precision of normal surveying measurements over short distances. Twenty-four states have legislated that surveying measures should be based on the US survey foot, eight have legislated that they be made on the basis of the international foot, eighteen have not specified the conversion factor from metric units; the most used area unit with a name unrelated to any length unit is the acre. The National Institute of Standards and Technology contends that customary area units are defined in terms of the square survey foot, not the square international foot.
Conversion factors are based on Astin and National Institute
The inch is a unit of length in the imperial and United States customary systems of measurement. It is equal to 1⁄12 of a foot. Derived from the Roman uncia, the word inch is sometimes used to translate similar units in other measurement systems understood as deriving from the width of the human thumb. Standards for the exact length of an inch have varied in the past, but since the adoption of the international yard during the 1950s and 1960s it has been based on the metric system and defined as 25.4 mm. The English word "inch" was an early borrowing from Latin uncia not present in other Germanic languages; the vowel change from Latin /u/ to Old English /y/ is known as umlaut. The consonant change from the Latin /k/ to English /tʃ/ is palatalisation. Both were features of Old English phonology. "Inch" is cognate with "ounce", whose separate pronunciation and spelling reflect its reborrowing in Middle English from Anglo-Norman unce and ounce. In many other European languages, the word for "inch" is the same as or derived from the word for "thumb", as a man's thumb is about an inch wide.
Examples include Afrikaans: duim. The inch is a used customary unit of length in the United States and the United Kingdom, it is used in Japan for electronic parts display screens. In most of continental Europe, the inch is used informally as a measure for display screens. For the United Kingdom, guidance on public sector use states that, since 1 October 1995, without time limit, the inch is to be used as a primary unit for road signs and related measurements of distance and may continue to be used as a secondary or supplementary indication following a metric measurement for other purposes; the international standard symbol for inch is in but traditionally the inch is denoted by a double prime, approximated by double quotes, the foot by a prime, approximated by an apostrophe. For example, three feet two inches can be written as 3′ 2″. Subdivisions of an inch are written using dyadic fractions with odd number numerators. 1 international inch is equal to: 10,000 tenths 1,000 thou or mil 100 points or gries 72 PostScript points 10, 12, 16, or 40 lines 6 computer picas 3 barleycorns 25.4 millimetres 0.999998 US Survey inches 1/3 or 0.333 palms 1/4 or 0.25 hands 1/12 or 0.08333 feet 1/36 or 0.02777 yards The earliest known reference to the inch in England is from the Laws of Æthelberht dating to the early 7th century, surviving in a single manuscript, the Textus Roffensis from 1120.
Paragraph LXVII sets out the fine for wounds of various depths: one inch, one shilling, two inches, two shillings, etc. An Anglo-Saxon unit of length was the barleycorn. After 1066, 1 inch was equal to 3 barleycorns, which continued to be its legal definition for several centuries, with the barleycorn being the base unit. One of the earliest such definitions is that of 1324, where the legal definition of the inch was set out in a statute of Edward II of England, defining it as "three grains of barley and round, placed end to end, lengthwise". Similar definitions are recorded in both Welsh medieval law tracts. One, dating from the first half of the 10th century, is contained in the Laws of Hywel Dda which superseded those of Dyfnwal, an earlier definition of the inch in Wales. Both definitions, as recorded in Ancient Laws and Institutes of Wales, are that "three lengths of a barleycorn is the inch". King David I of Scotland in his Assize of Weights and Measures is said to have defined the Scottish inch as the width of an average man's thumb at the base of the nail including the requirement to calculate the average of a small, a medium, a large man's measures.
However, the oldest surviving manuscripts date from the early 14th century and appear to have been altered with the inclusion of newer material. In 1814, Charles Butler, a mathematics teacher at Cheam School, recorded the old legal definition of the inch to be "three grains of sound ripe barley being taken out the middle of the ear, well dried, laid end to end in a row", placed the barleycorn, not the inch, as the base unit of the English Long Measure system, from which all other units were derived. John Bouvier recorded in his 1843 law dictionary that the barleycorn was the fundamental measure. Butler observed, that "s the length of the barley-corn cannot be fixed, so the inch according to this method will be uncertain", noting that a standard inch measure was now kept in the Exchequer chamber and, the legal definition of the inch; this was a point made by George Long in his 1842 Penny Cyclopædia, observing that st
A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or fraction of the unit. While all metric prefixes in common use today are decadic there have been a number of binary metric prefixes as well; each prefix has a unique symbol, prepended to the unit symbol. The prefix kilo-, for example, may be added to gram to indicate multiplication by one thousand: one kilogram is equal to one thousand grams; the prefix milli- may be added to metre to indicate division by one thousand. Decimal multiplicative prefixes have been a feature of all forms of the metric system, with six of these dating back to the system's introduction in the 1790s. Metric prefixes have been used with some non-metric units; the SI prefixes are standardized for use in the International System of Units by the International Bureau of Weights and Measures in resolutions dating from 1960 to 1991. Since 2009, they have formed part of the International System of Quantities; the BIPM specifies twenty prefixes for the International System of Units.
Each prefix name has a symbol, used in combination with the symbols for units of measure. For example, the symbol for'kilo-' is'k', is used to produce'km','kg', and'kW', which are the SI symbols for kilometre and kilowatt, respectively. Where the Greek letter'μ' is unavailable, the symbol for micro'µ' may be used. Where both variants are unavailable, the micro prefix is written as the lowercase Latin letter'u'. Prefixes corresponding to an integer power of one thousand are preferred. Hence'100 m' is preferred over'1 hm' or'10 dam'; the prefixes hecto, deca and centi are used for everyday purposes, the centimetre is common. However, some modern building codes require that the millimetre be used in preference to the centimetre, because "use of centimetres leads to extensive usage of decimal points and confusion". Prefixes may not be used in combination; this applies to mass, for which the SI base unit contains a prefix. For example, milligram is used instead of microkilogram. In the arithmetic of measurements having units, the units are treated as multiplicative factors to values.
If they have prefixes, all but one of the prefixes must be expanded to their numeric multiplier, except when combining values with identical units. Hence, 5 mV × 5 mA = 5×10−3 V × 5×10−3 A = 25×10−6 V⋅A = 25 μW 5.00 mV + 10 μV = 5.00 mV + 0.01 mV = 5.01 mVWhen powers of units occur, for example, squared or cubed, the multiplication prefix must be considered part of the unit, thus included in the exponentiation. 1 km2 means one square kilometre, or the area of a square of 1000 m by 1000 m and not 1000 square metres. 2 Mm3 means two cubic megametres, or the volume of two cubes of 1000000 m by 1000000 m by 1000000 m or 2×1018 m3, not 2000000 cubic metres. Examples5 cm = 5×10−2 m = 5 × 0.01 m = 0.05 m 9 km2 = 9 × 2 = 9 × 2 × m2 = 9×106 m2 = 9 × 1000000 m2 = 9000000 m2 3 MW = 3×106 W = 3 × 1000000 W = 3000000 W The use of prefixes can be traced back to the introduction of the metric system in the 1790s, long before the 1960 introduction of the SI. The prefixes, including those introduced after 1960, are used with any metric unit, whether included in the SI or not.
Metric prefixes may be used with non-metric units. The choice of prefixes with a given unit is dictated by convenience of use. Unit prefixes for amounts that are much larger or smaller than those encountered are used; the units kilogram, milligram and smaller are used for measurement of mass. However, megagram and larger are used. Megagram and teragram are used to disambiguate the metric tonne from other units with the name'ton'; the kilogram is the only base unit of the International System of Units that includes a metric prefix. The litre, millilitre and smaller are common. In Europe, the centilitre is used for packaged products such as wine and the decilitre is less frequently; the latter two items include prefixes corresponding to an exponent, not divisible by three. Larger volumes are denoted in kilolitres, megalitres or gigalitres, or else in cubic metres or cubic kilometres. For scientific purposes, the cubic metre is used; the kilometre, centimetre and smaller are common. The micrometre is referred to by the non-SI term micron.
In some fields, such as chemistry, the ångström competed with the nanometre. The femtometre, used in particle physics, is sometimes called a fermi. For large scales, megametre and larger are used. Instead, non-metric units are used, such as astronomical units, light years, parsecs; the second, millisecond and shorter are common. The kilosecond and megasecond have some use, though for these and longer times one uses either scientific notation or minutes, so on; the SI unit of angle is the radian, but degrees and seconds see some scientific use. Official policy varies from common practice for the degree Celsius. NIST states: "Prefix symbols may be used with the unit symbol °C and prefix names may be used with the unit name'degree Celsius'. For example, 12 m°C (12 millidegr
The kilometre, or kilometer is a unit of length in the metric system, equal to one thousand metres. It is now the measurement unit used for expressing distances between geographical places on land in most of the world. K is used in some English-speaking countries as an alternative for the word kilometre in colloquial writing and speech. A slang term for the kilometre in the US and UK military is klick. There are two common pronunciations for the word; the former follows a pattern in English whereby metric units are pronounced with the stress on the first syllable and the pronunciation of the actual base unit does not change irrespective of the prefix. It is preferred by the British Broadcasting Corporation and the Australian Broadcasting Corporation. Many scientists and other users in countries where the metric system is not used, use the pronunciation with stress on the second syllable; the latter pronunciation follows the stress pattern used for the names of measuring instruments. The problem with this reasoning, however, is that the word meter in those usages refers to a measuring device, not a unit of length.
The contrast is more obvious in countries using the British rather than American spelling of the word metre. When Australia introduced the metric system in 1975, the first pronunciation was declared official by the government's Metric Conversion Board. However, the Australian prime minister at the time, Gough Whitlam, insisted that the second pronunciation was the correct one because of the Greek origins of the two parts of the word. By the 8 May 1790 decree, the Constituent assembly ordered the French Academy of Sciences to develop a new measurement system. In August 1793, the French National Convention decreed the metre as the sole length measurement system in the French Republic; the first name of the kilometre was "Millaire". Although the metre was formally defined in 1799, the myriametre was preferred to the "kilometre" for everyday use; the term "myriamètre" appeared a number of times in the text of Develey's book Physique d'Emile: ou, Principes de la science de la nature, while the term kilometre only appeared in an appendix.
French maps published in 1835 had scales showing myriametres and "lieues de Poste". The Dutch gave it the local name of the mijl, it was only in 1867 that the term "kilometer" became the only official unit of measure in the Netherlands to represent 1000 metres. Two German textbooks dated 1842 and 1848 give a snapshot of the use of the kilometre across Europe - the kilometre was in use in the Netherlands and in Italy and the myriametre was in use in France. In 1935, the International Committee for Weights and Measures abolished the prefix "myria-" and with it the "myriametre", leaving the kilometre as the recognised unit of length for measurements of that magnitude. In the United Kingdom, road signs show distances in miles and location marker posts that are used for reference purposes by road engineers and emergency services show distance references in unspecified units which are kilometre-based; the advent of the mobile phone has been instrumental in the British Department for Transport authorising the use of driver location signs to convey the distance reference information of location marker posts to road users should they need to contact the emergency services.
In the US, the National Highway System Designation Act of 1995 prohibits the use of federal-aid highway funds to convert existing signs or purchase new signs with metric units. The Executive Director of the US Federal Highway Administration, Jeffrey Paniati, wrote in a 2008 memo: "Section 205 of the National Highway System Designation Act of 1995 prohibited us from requiring any State DOT to use the metric system during project development activities. Although the State DOT's had the option of using metric measurements or dual units, all of them abandoned metric measurements and reverted to sole use of inch-pound values." The Manual on Uniform Traffic Control Devices since 2000 is published in both metric and American Customary Units. Some sporting disciplines feature 1000 m races in major events, but in other disciplines though world records are catalogued, the one kilometre event remains a minority event; the world records for various sporting disciplines are: Conversion of units, for comparison with other units of length Cubic metre Metric prefix Mileage Odometer Orders of magnitude Square kilometre Media related to Distance indicators at Wikimedia Commons
An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its directional flight controls. Some other aircrew members, such as navigators or flight engineers, are considered aviators, because they are involved in operating the aircraft's navigation and engine systems. Other aircrew members, such as flight attendants and ground crew, are not classified as aviators. In recognition of the pilots' qualifications and responsibilities, most militaries and many airlines worldwide award aviator badges to their pilots; the first recorded use of the term aviator was in 1887, as a variation of "aviation", from the Latin avis, coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne. The term aviatrix, now archaic, was used for a female aviator; these terms were used more in the early days of aviation, when airplanes were rare, connoted bravery and adventure. For example, a 1905 reference work described the Wright brothers' first airplane: "The weight, including the body of the aviator, is a little more than 700 pounds".
To ensure the safety of people in the air and on the ground, early aviation soon required that aircraft be under the operational control of a properly trained, certified pilot at all times, responsible for the safe and legal completion of the flight. The Aéro-Club de France delivered the first certificate to Louis Blériot in 1908—followed by Glenn Curtiss, Léon Delagrange, Robert Esnault-Pelterie; the British Royal Aero Club followed in 1910 and the Aero Club of America in 1911. Civilian pilots fly aircraft of all types for pleasure, charity, or in pursuance of a business, or commercially for non-scheduled and scheduled passenger and cargo air carriers, corporate aviation, forest fire control, law enforcement, etc; when flying for an airline, pilots are referred to as airline pilots, with the pilot in command referred to as the captain. There are 290,000 airline pilots in the world in 2017 and aircraft simulator manufacturer CAE Inc. forecasts a need for 255,000 new ones for a population of 440,000 by 2027, 150,000 for growth and 105,000 to offset retirement and attrition: 90,000 in Asia-Pacific, 85,000 in Americas, 50,000 in Europe and 30,000 in Middle East & Africa.
Boeing expects 790,000 new pilots in 20 years from 2018, 635,000 for commercial aviation, 96,000 for business aviation and 59,000 for helicopters: 33% in Asia Pacific, 26% in North America, 18% in Europe, 8% in the Middle East, 7% in Latin America, 4% in Africa and 3% in Russia/ Central Asia. By November 2017, due a shortage of qualified pilots, some pilots are leaving corporate aviation to return to airlines. In one example a Global 6000 pilot, making $250,000 a year for 10 to 15 flight hours a month, returned to American Airlines with full seniority. A Gulfstream G650 or Global 6000 pilot might earn between $245,000 and $265,000, recruiting one may require up to $300,000. At the other end of the spectrum, constrained by the available pilots, some small carriers hire new pilots who need 300 hours to jump to airlines in a year, they may recruit non-career pilots who have other jobs or airline retirees who want to continue to fly. The number of airline pilots could decrease as automation replaces copilots and pilots as well.
In January 2017 Rhett Ross, CEO of Continental Motors said "my concern is that in the next two decades—if not sooner—automated and autonomous flight will have developed sufficiently to put downward pressure on both wages and the number and kind of flying jobs available. So if a kid asks the question now and he or she is 18, 20 years from now will be 2037 and our would-be careerist will be 38—not mid-career. Who among us thinks aviation and for-hire flying will look like it does now?" Christian Dries, owner of Diamond Aircraft Austria said "Behind the curtain, aircraft manufacturers are working on a single-pilot cockpit where the airplane can be controlled from the ground and only in case of malfunction does the pilot of the plane interfere. The flight will be autonomous and I expect this to happen in the next five to six years for freighters."In August 2017 financial company UBS predicted pilotless airliners are technically feasible and could appear around 2025, offering around $35bn of savings in pilot costs: $26bn for airlines, $3bn for business jets and $2.1bn for civil helicopters.
Regulations have to adapt with air cargo at the forefront, but pilotless flights could be limited by consumer behaviour: 54% of 8,000 people surveyed are defiant while 17% are supportive, with acceptation progressively forecast. AVweb reporter Geoff Rapoport stated, "pilotless aircraft are an appealing prospect for airlines bracing for the need to hire several hundred thousand new pilots in the next decade. Wages and training costs have been rising at regional U. S. airlines over the last several years as the major airlines have hired pilots from the regionals at unprecedented rates to cover increased air travel demand from economic expansion and a wave of retirements". Going to pilotless airliners could be done in one bold step or in gradual improvements like by reducing the cockpit crew for long haul missions or allowing single pilot cargo aircraft; the industry has not decided
The United Kingdom the United Kingdom of Great Britain and Northern Ireland, sometimes referred to as Britain, is a sovereign country located off the north-western coast of the European mainland. The United Kingdom includes the island of Great Britain, the north-eastern part of the island of Ireland, many smaller islands. Northern Ireland is the only part of the United Kingdom that shares a land border with another sovereign state, the Republic of Ireland. Apart from this land border, the United Kingdom is surrounded by the Atlantic Ocean, with the North Sea to the east, the English Channel to the south and the Celtic Sea to the south-west, giving it the 12th-longest coastline in the world; the Irish Sea lies between Great Ireland. With an area of 242,500 square kilometres, the United Kingdom is the 78th-largest sovereign state in the world, it is the 22nd-most populous country, with an estimated 66.0 million inhabitants in 2017. The UK is constitutional monarchy; the current monarch is Queen Elizabeth II, who has reigned since 1952, making her the longest-serving current head of state.
The United Kingdom's capital and largest city is London, a global city and financial centre with an urban area population of 10.3 million. Other major urban areas in the UK include Greater Manchester, the West Midlands and West Yorkshire conurbations, Greater Glasgow and the Liverpool Built-up Area; the United Kingdom consists of four constituent countries: England, Scotland and Northern Ireland. Their capitals are London, Edinburgh and Belfast, respectively. Apart from England, the countries have their own devolved governments, each with varying powers, but such power is delegated by the Parliament of the United Kingdom, which may enact laws unilaterally altering or abolishing devolution; the nearby Isle of Man, Bailiwick of Guernsey and Bailiwick of Jersey are not part of the UK, being Crown dependencies with the British Government responsible for defence and international representation. The medieval conquest and subsequent annexation of Wales by the Kingdom of England, followed by the union between England and Scotland in 1707 to form the Kingdom of Great Britain, the union in 1801 of Great Britain with the Kingdom of Ireland created the United Kingdom of Great Britain and Ireland.
Five-sixths of Ireland seceded from the UK in 1922, leaving the present formulation of the United Kingdom of Great Britain and Northern Ireland. There are fourteen British Overseas Territories, the remnants of the British Empire which, at its height in the 1920s, encompassed a quarter of the world's land mass and was the largest empire in history. British influence can be observed in the language and political systems of many of its former colonies; the United Kingdom is a developed country and has the world's fifth-largest economy by nominal GDP and ninth-largest economy by purchasing power parity. It has a high-income economy and has a high Human Development Index rating, ranking 14th in the world, it was the world's first industrialised country and the world's foremost power during the 19th and early 20th centuries. The UK remains a great power, with considerable economic, military and political influence internationally, it is sixth in military expenditure in the world. It has been a permanent member of the United Nations Security Council since its first session in 1946.
It has been a leading member state of the European Union and its predecessor, the European Economic Community, since 1973. The United Kingdom is a member of the Commonwealth of Nations, the Council of Europe, the G7, the G20, NATO, the Organisation for Economic Co-operation and Development and the World Trade Organization; the 1707 Acts of Union declared that the kingdoms of England and Scotland were "United into One Kingdom by the Name of Great Britain". The term "United Kingdom" has been used as a description for the former kingdom of Great Britain, although its official name from 1707 to 1800 was "Great Britain"; the Acts of Union 1800 united the kingdom of Great Britain and the kingdom of Ireland in 1801, forming the United Kingdom of Great Britain and Ireland. Following the partition of Ireland and the independence of the Irish Free State in 1922, which left Northern Ireland as the only part of the island of Ireland within the United Kingdom, the name was changed to the "United Kingdom of Great Britain and Northern Ireland".
Although the United Kingdom is a sovereign country, Scotland and Northern Ireland are widely referred to as countries. The UK Prime Minister's website has used the phrase "countries within a country" to describe the United Kingdom; some statistical summaries, such as those for the twelve NUTS 1 regions of the United Kingdom refer to Scotland and Northern Ireland as "regions". Northern Ireland is referred to as a "province". With regard to Northern Ireland, the descriptive name used "can be controversial, with the choice revealing one's political preferences"; the term "Great Britain" conventionally refers to the island of Great Britain, or politically to England and Wales in combination. However, it is sometimes used as a loose synonym for the United Kingdom as a whole; the term "Britain" is used both as a synonym for Great Britain, as a synonym for the United Kingdom. Usage is mixed, with the BBC preferring to use Britain as shorthand only for Great Britain and the UK Government, while accepting that both terms refer to the United K
Orders of magnitude (length)
The following are examples of orders of magnitude for different lengths. To help compare different orders of magnitude, the following list describes various lengths between 1.6 × 10 − 35 metres and 10 10 10 122 metres. To help compare different orders of magnitude, this section lists lengths shorter than 10−23 m. 1.6 × 10−11 yoctometres – the Planck length. 1 ym – 1 yoctometre, the smallest named subdivision of the metre in the SI base unit of length, one septillionth of a metre 1 ym – length of a neutrino. 2 ym – the effective cross-section radius of 1 MeV neutrinos as measured by Clyde Cowan and Frederick Reines To help compare different orders of magnitude, this section lists lengths between 10−23 metres and 10−22 metres. To help compare different orders of magnitude, this section lists lengths between 10−22 m and 10−21 m. 100 ym – length of a top quark, one of the smallest known quarks To help compare different orders of magnitude, this section lists lengths between 10−21 m and 10−20 m. 2 zm – length of a preon, hypothetical particles proposed as subcomponents of quarks and leptons.
2 zm – radius of effective cross section for a 20 GeV neutrino scattering off a nucleon 7 zm – radius of effective cross section for a 250 GeV neutrino scattering off a nucleon To help compare different orders of magnitude, this section lists lengths between 10−20 m and 10−19 m. 15 zm – length of a high energy neutrino 30 zm – length of a bottom quark To help compare different orders of magnitude, this section lists lengths between 10−19 m and 10−18 m. 177 zm – de Broglie wavelength of protons at the Large Hadron Collider To help compare different orders of magnitude, this section lists lengths between 10−18 m and 10−17 m. 1 am – sensitivity of the LIGO detector for gravitational waves 1 am – upper limit for the size of quarks and electrons 1 am – upper bound of the typical size range for "fundamental strings" 1 am – length of an electron 1 am – length of an up quark 1 am – length of a down quark To help compare different orders of magnitude, this section lists lengths between 10−17 m and 10−16 m. 10 am – range of the weak force To help compare different orders of magnitude, this section lists lengths between 10−16 m and 10−15 m. 100 am – all lengths shorter than this distance are not confirmed in terms of size 850 am – approximate proton radius The femtometre is a unit of length in the metric system, equal to 10−15 metres.
In particle physics, this unit is more called a fermi with abbreviation "fm". To help compare different orders of magnitude, this section lists lengths between 10−15 metres and 10−14 metres. 1 fm – length of a neutron 1.5 fm – diameter of the scattering cross section of an 11 MeV proton with a target proton 1.75 fm – the effective charge diameter of a proton 2.81794 fm – classical electron radius 7 fm – the radius of the effective scattering cross section for a gold nucleus scattering a 6 MeV alpha particle over 140 degrees To help compare different orders of magnitude, this section lists lengths between 10−14 m and 10−13 m. 1.75 to 15 fm – Diameter range of the atomic nucleus To help compare different orders of magnitude, this section lists lengths between 10−13 m and 10−12 m. 570 fm – typical distance from the atomic nucleus of the two innermost electrons in the uranium atom, the heaviest naturally-occurring atom To help compare different orders of magnitude this section lists lengths between 10−12 and 10−11 m. 1 pm – distance between atomic nuclei in a white dwarf 2.4 pm – The Compton wavelength of the electron 5 pm – shorter X-ray wavelengths To help compare different orders of magnitude this section lists lengths between 10−11 and 10−10 m. 25 pm – approximate radius of a helium atom, the smallest neutral atom 50 pm – radius of a hydrogen atom 50 pm – bohr radius: approximate radius of a hydrogen atom ~50 pm – best resolution of a high-resolution transmission electron microscope 60 pm – radius of a carbon atom 93 pm – length of a diatomic carbon molecule To help compare different orders of magnitude this section lists lengths between 10−10 and 10−9 m. 100 pm – 1 ångström 100 pm – covalent radius of sulfur atom 120 pm – van der Waals radius of a neutral hydrogen atom 120 pm – radius of a gold atom 126 pm – covalent radius of ruthenium atom 135 pm – covalent radius of technetium atom 150 pm – Length of a typical covalent bond 153 pm – covalent radius of silver atom 155 pm – covalent radius of zirconium atom 175 pm – covalent radius of thulium atom 200 pm – highest resolution of a typical electron microscope 225 pm – covalent radius of caesium atom 280 pm – Average size of the water molecule 298 pm – radius of a caesium atom, calculated to be the largest atomic radius 340 pm – thickness of single layer graphene 356.68 pm – width of diamond unit cell 403 pm – width of lithium fluoride unit cell 500 pm – Width of protein α helix 543 pm – silicon lattice spacing 560 pm – width of sodium chloride unit cell 700 pm – width of glucose molecule 780 pm – mean width of quartz unit cell 820 pm – mean width of ice unit cell 900 pm – mean width of coesite unit cell To help compare different orders