Rule of thumb · MathematicsNº 110 / 167

Area scales with the square, volume with the cube

Double every dimension of a shape and its area quadruples while its volume grows eightfold — the exponent, not the shape, decides how fast size compounds.

Why it works

This is why small animals lose heat faster relative to their mass (surface area) than large ones, and why doubling a tank’s dimensions needs eight times the material to hold eight times the liquid, not twice.

When it fails

Only under uniform scaling. Stretch one dimension and the exponents no longer apply. It is also why scale models mislead: doubling an animal's height multiplies its weight eightfold but its bone cross-section only fourfold, which is the reason a mouse enlarged to elephant size would collapse.

Do it exactly

Estimate with the rule, then check it against the calculator that models it properly.

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If you double the size, what happens to area and volume?

Double every dimension of a shape and its area quadruples while its volume grows eightfold — the exponent, not the shape, decides how fast size compounds. This is why small animals lose heat faster relative to their mass (surface area) than large ones, and why doubling a tank’s dimensions needs eight times the material to hold eight times the liquid, not twice.

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