Polymer Clay Shrinkage Calculator

Polymer clay shrinks slightly on baking as plasticiser cooks off, not moisture — brand-dependent, roughly 3% for Premo and 1–2% for Fimo. Starting from a target finished size, shape the raw piece larger by that rate.

Your numbers

Finished size(cm)Shrinkage(%)

Pre-bake size

5.15cm

Formula

Pre-bake size = Finished size ÷ (1 − Shrinkage ÷ 100)

Shrinkage varies a little by colour and batch even within one brand. Bake a small test piece first if this is a colour you have not used before.

What to enter

Input	Default	Accepted range
Finished size (cm)	5	0.5 and up
Shrinkage (%)How much it shrank; pre-washing spends this before you cut.	3	0 ~ 8

Step by step

FormulaPre-bake size = Finished size ÷ (1 − Shrinkage ÷ 100)

With the default numbersPre-bake size = 5 ÷ (1 − 3 ÷ 100)

AnswerPre-bake size = 5.15 cm

Quick reference table

Results when only Finished size (cm) changes and everything else stays put.

Finished size (cm)	Pre-bake size (cm)
2.5	2.58
3.75	3.87
5	5.15
7.5	7.73
10	10.31

What each result means

Result	At default values
Pre-bake size (cm)The larger size you shape before baking, ahead of the finished size, to allow for shrinkage.	5.15

Common mistakes

Shrinkage varies a little by colour and batch even within one brand. Bake a small test piece first if this is a colour you have not used before.

Glossary

Shrinkage: How much it shrank; pre-washing spends this before you cut.
Pre-bake size: The larger size you shape before baking, ahead of the finished size, to allow for shrinkage.

Frequently asked questions

QHow is Polymer Clay Shrinkage Calculator calculated?

Pre-bake size = Finished size ÷ (1 − Shrinkage ÷ 100) — Polymer clay shrinks slightly on baking as plasticiser cooks off, not moisture — brand-dependent, roughly 3% for Premo and 1–2% for Fimo. Starting from a target finished size, shape the raw piece larger by that rate.

QCan you walk through an example?

With Finished size 5cm, Shrinkage 3%, the answer is Pre-bake size 5.15cm.

QWhat do I need to enter?

Enter Finished size, Shrinkage. The result recalculates as you type, and an empty box counts as zero.

QHow much does the answer move if I change a number?

Changing only Finished size (cm) moves the answer to Finished size (cm) 2.5 → Pre-bake size (cm) 2.58 and Finished size (cm) 10 → Pre-bake size (cm) 10.31. The table below lays out five steps.

QHow are the numbers rounded?

Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.

QAnything to watch out for?

Shrinkage varies a little by colour and batch even within one brand. Bake a small test piece first if this is a colour you have not used before.

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Materials differ in density and absorption. If your label states a figure, use it — the defaults here are only common values.