Kleiber's law
Kleiber's law, named after Max Kleiber for his biology work in the early 1930s, states, after many observations that, for a vast number of animals, an animal's Basal Metabolic Rate scales to the 3⁄4 power of the animal's mass.
More precisely : posing w = mass of the animal in kilograms, then BMR = 70w kilocalories per day, or BMR = 3.4w watts.
Thus, over the same time span, a cat having a mass 100 times that of a mouse will consume only about 32 times the energy the mouse uses.
It is presently unclear if the value of the exponent in Kleiber's law is correct, in part because the law currently lacks a single theoretical explanation that is entirely satisfactory.
More recently, Kleiber's law has also been shown to apply in plants, suggesting that Kleiber's observation is much more general.