Biology

Why an elephant doesn't eat 200,000 times more than a mouse: Kleiber's three-quarter law

A log-log chart with a green line rising from a small dot for a 20 gram mouse to a large dot for a 4 tonne elephant, slightly flatter than a dashed proportional line
30seconds
The 30-second version

A mouse is 200,000 times lighter than an elephant, yet the elephant burns only about 9,000 times more energy. In 1932 Max Kleiber found that resting metabolic rate grows as body mass to the power of about three quarters, so every kilogram of a big animal runs cooler than a kilogram of a small one.

Drag the dot along the line, from mouse to elephant, and change the exponent to see what the surface-area rule and strict proportionality would predict. Then watch the heart slow, the lifespan stretch and the lifetime beat count barely move.

Deep dive · 5 min
Deep dive · 5 min

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