The clay shrinkage formula
A clay body that shrinks 12.5% retains 87.5% of its wet size. To estimate the fired size, multiply by 0.875. To work backward from the finished dimension, divide by 0.875.
wet = fired ÷ (1 − shrinkage ÷ 100)
The key mistake to avoid: adding the shrinkage percentage directly to the fired size gives the wrong answer. A 100 mm piece with 12.5% shrinkage needs a wet form of 114.29 mm—not 112.5 mm.
How to use this clay shrinkage calculator
Select your conversion direction (Wet → Fired or Fired → Wet), enter your measurement and shrinkage percentage, and read the result. Supplier figures are useful starting points, but your forming method, drying, firing schedule, and clay batch can change the result. Use a test bar to measure your own clay's actual shrinkage for work that must fit precisely.
What is clay shrinkage?
Clay shrinks during drying and again during firing as the water burns off and the silica particles fuse. Total shrinkage—from wet to fully fired—is typically between 7% (earthenware) and 14% (porcelain). See the clay shrinkage chart for common clay body estimates.