MENTAL MODEL · M5645

Kleiber's Law

SystemsHigh supportSystems Theory

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Version 1.0.0 · Updated 2026-07-30

CORE DEFINITION

An animal's metabolic rate is proportional to the 3/4 power of its body mass. This means that larger animals have lower energy expenditure per unit of body weight (higher efficiency). A cat is 100 times heavier than a mouse but has a metabolic rate only 32 times that of a mouse.

SCAFFOLDING EFFECT

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The efficiency dividend of scale. This is why cities and businesses pursue scale: every time scale doubles, the 'infrastructure energy' required to maintain the system does not double but grows with an exponent of 0.75. The energy saved is the profit of scale.

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Metabolic rate B ∝ M^(3/4). As scale increases, energy consumption per unit mass decreases sublinearly, producing 'economies of scale'—infrastructure and energy demand grow slower than scale.

MINIMUM ACTION

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Practice this model in one real situation:

Determine whether a system exhibits scale effects (exponent ≈ 0.75)
Expect decreasing unit costs during expansion
Leverage scale dividends but guard against rigidity
Identify better exponents (cities ≈ 1.15 superlinear)
Exploit before critical points, be wary after.

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Source support: Explicit

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zh.wikipedia.orghttps://zh.wikipedia.org/wiki/%E5%85%8B%E8%8E%B1%E4%BC%AF%E5%AE%9A%E5%BE%8BZH · Explicit
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