Find your clay body's shrinkage rate from wet and fired measurements, or plan how big to make a piece to hit a target fired size.
Clay shrinks twice — once as it dries, and again in the kiln. If you don't account for it, pieces come out smaller than you planned: a mug holds less than intended, a lid no longer fits its jar, tiles end up undersized. A little maths up front saves a lot of disappointment.
This calculator works two ways. In Measure mode, enter a wet measurement and the matching dry or fired measurement and it returns the shrinkage percentage. In Plan mode, enter the fired size you want plus your known shrinkage rate, and it tells you how big to make the piece while it's still wet.
To measure your own rate, mark a known length on a fresh test bar — say 100 mm — then measure again after firing. The difference, as a percentage, is your shrinkage rate. It varies by clay body and firing temperature, so it's worth testing each clay you use.
Related: What is clay shrinkage? · All tools
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