Free tools for artists
Clay shrinkage calculator
Clay shrinks as it dries and again in every firing. Enter the size you want the finished piece to be, and this works out how big to make it while the clay is still wet.
Results
Wet clay sizes
Enter a finished size and a shrinkage figure, then press Calculate wet sizes.
How it works
Divide, don't add
Shrinkage is a share of the wet size, so divide the finished size by what is left.
A bowl to finish at 25 cm, in a clay that shrinks 12%:
25 ÷ 0.88 = 28.41 cm comes out at 25 cm
25 + 12% = 28 cm comes out at 24.64 cm, too small
Stages multiply
Drying, bisque and glaze each shrink what the stage before left.
6% · 4% · 3% → 12.47% not 13%
Measure your own
Mark a 10 cm line on a wet test tile and measure it again after the glaze firing. It knows how you work and how hot your kiln really fires.
10 cm → 8.8 cm = 12% (wet − fired) ÷ wet × 100
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