Clay Shrinkage Calculator for Pottery
Clay shrinks as it dries and fires. Enter your clay's shrinkage rate and either the wet size or the fired size you want, and this works out the matching dimension and the shrinkage factor.
How to calculate clay shrinkage
- Enter your clay body's total shrinkage percent.
- Enter either the wet (greenware) size or the target fired size.
- Read the matching size and shrinkage factor, then copy the result.
Examples
12% shrinkage on a 10 unit wet piece
12% shrinkage, wet size 10
Fired size 8.8, shrinkage factor 0.88
Frequently asked questions
How do I find my clay's shrinkage rate?
Make a test tile, mark a line of known length (for example 10 cm) on it wet, then fire it to your usual cone and measure again. Shrinkage percent is the lost length divided by the original, times 100.
How do I size a wet piece to hit a fired dimension?
Enter the shrinkage percent and the fired size you want. The tool divides by the shrinkage factor to give the wet size to build, so the piece lands on target after firing.
What is the shrinkage factor?
It is the multiplier from wet to fired, equal to 1 minus shrinkage over 100. At 12% shrinkage the factor is 0.88, so a wet length is multiplied by 0.88 to get the fired length.
Does shrinkage depend on the firing temperature?
Yes. The same clay usually shrinks more at a higher cone as it matures further. Measure shrinkage at the cone you actually fire to for the most accurate result.
Does this work for any unit?
Yes. Shrinkage is a ratio, so the wet and fired sizes come out in whatever unit you enter, whether millimeters, centimeters or inches.
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