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Material shrinkage calculator

Enter the size you know — either the target final size or the mold/blank size — and the material's shrinkage percentage. The calculator works out both sizes and the shrinkage allowance.

Look up the material's data sheet: casting alloys and plastics are usually 0.5–2%, wood on drying is 3–10% depending on species and grain direction

Result

Shrinkage allowance

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Mold / blank size —
Final size after shrinkage —

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This calculation is for informational purposes only and does not replace advice from a qualified professional. Formulas and rates may not fit your exact situation — double-check the figures before making decisions.

How it is calculated

If you know the target final size, mold size = final size ÷ (1 − shrinkage ÷ 100) — larger than the target, because the material in the mold is bigger than what remains after it shrinks.

If you know the mold or blank size, final size = mold size × (1 − shrinkage ÷ 100) — the material shrinks by that percentage on cooling, curing or drying.

Shrinkage allowance = mold size − final size. Get the shrinkage percentage for your specific material from its data sheet or a trial casting/blank — reference values give the right order of magnitude, but a specific batch of raw material can differ.

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