Clay Shrinkage Calculator
Built by Johnny Alto · free, no sign-up · updated July 26, 2026
Clay shrinks as it dries and again when fired, so a pot always ends up smaller than you threw it. Use this to work out the wet size to make for a target fired size, the fired size from a wet size, or to measure your own clay's shrinkage rate from a test tile.
Make it this wet size0same units you entered
Measure your own clay's shrinkage
Your shrinkage rate0%wet to fired
Draw a 10 cm line on a wet test tile, fire it through your normal cycle, then measure the line again. Shrinkage varies by clay body and firing temperature, usually 10 to 13 percent for stoneware, so measure your own for accuracy.
Why clay shrinks, and by how much
Clay shrinks twice on its way to a finished pot. First as it dries and the water between the clay particles leaves, then again in the kiln as the clay body tightens and vitrifies. The two together are the total shrinkage rate, and for most stoneware it lands between 10 and 13 percent, though it varies by clay body and how hot you fire.
To hit a target fired size you have to make the piece larger to begin with. Divide the fired size you want by one minus the shrinkage rate to get the wet size to throw or build. Going the other way, multiply a wet measurement by one minus the rate to predict the fired size.
Measure your own shrinkage
Published rates are a starting point, but your clay and your kiln are what matter. Scratch or draw a line exactly ten centimeters long on a wet test tile, let it dry, fire it through your normal cycle, then measure the line again. The difference as a percentage of the original is your true shrinkage rate, and using it will make your sizing far more reliable, which matters most for lids, tiles, and anything that has to fit.
Recommended gear
Pottery gear for the studio
Frequently asked questions
How do I calculate clay shrinkage?
To find the wet size for a target fired size, divide the fired size by one minus the shrinkage rate. For a 12 percent clay, an 8 inch fired bowl needs to be made about 9.1 inches wet.
How much does clay shrink?
Most stoneware shrinks 10 to 13 percent from wet to fired, combining drying and firing shrinkage. It varies by clay body and firing temperature, so measure your own for accuracy.
How do I measure my clay's shrinkage rate?
Draw a 10 cm line on a wet test tile, fire it normally, and measure the line again. The reduction as a percentage of the original length is your shrinkage rate.
Why does shrinkage matter for lids?
Because parts that must fit, like lids, tiles, and gallery seats, only work if you account for shrinkage. Small errors in the rate become visible gaps once fired.
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This calculator gives estimates for planning only; always confirm against your own measurements and species research. Some links are to our buying guides, which contain affiliate links. As an Amazon Associate I earn from qualifying purchases.
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