Kleiber's Law

Kleiber’s Law says that whole-body metabolic rate increases with body mass, but less than proportionally: doubling an animal’s mass does not double its energy use. The 0.75 exponent reflects a biological scaling pattern linked to how transport networks, heat loss, and resource distribution become less efficient as organisms get larger, so larger animals use more energy in total but less per kilogram. The constant 70 sets the scale of the rate for a 1 kg body mass in the chosen units, while M is the animal’s mass in kilograms.

Use this when estimating the basal metabolic rate of mammals or comparing how energy demand changes across species of different sizes. It is also useful in ecology, physiology, and allometric scaling problems where you need a realistic estimate of resting metabolism from body mass.

• Assuming metabolic rate scales linearly with mass instead of using the 0.75 exponent
• Forgetting that M must be in kilograms before substituting into the formula
• Treating the constant 70 as universal for every organism and every context, rather than an approximate empirical constant for the model