The square–cube law is a mathematical principle, applied in a variety of scientific fields, which describes the relationship between the volume and the surface area as a shape's size increases or decreases. It was first described in 1638 by Galileo Galilei in his Two New Sciences as the "...ratio of two volumes is greater than the ratio of their surfaces".

The surface-area-to-volume ratio or surface-to-volume ratio is the ratio between surface area and volume of an object or collection of objects.