🏺 Clay Shrinkage Calculator

Apply your clay body's shrinkage rate to find the greenware size needed for a target fired size, or predict the fired size from a greenware size.

Greenware Size Needed

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GUIDE

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Why Does Clay Shrink?

Clay shrinks in two stages: first during drying, as water leaves the clay body, and again during firing, as the particles fuse more tightly together. The combined total shrinkage varies a great deal by clay body, but the following approximate ranges are commonly published (actual values vary by manufacturer and firing temperature).

Clay Body	Approx. Total Shrinkage
Earthenware	~5-8%
Stoneware	~10-13%
Porcelain	~12-20%

Shrinkage Calculation Formulas

Assuming shrinkage is roughly linear and isotropic (similar in all directions) for a well-behaved clay body, use the following formulas.

Mode A: Target Fired Size → Greenware Size
Greenware size = Fired size ÷ (1 − Shrinkage rate/100)
Example: for a target fired length of 20cm at a 12% shrinkage rate (stoneware), you need a greenware size of 20 ÷ 0.88 ≈ 22.73cm.

Mode B: Greenware Size → Predicted Fired Size
Fired size = Greenware size × (1 − Shrinkage rate/100)
Example: a greenware length of 22.73cm at 12% shrinkage gives a predicted fired size of 22.73 × 0.88 ≈ 20.00cm — the exact inverse of Mode A.

Frequently asked questions

Does shrinkage happen equally in width, length, and height?

This calculator assumes isotropic shrinkage (the same in every direction) to keep the math simple. In practice, wedging direction, forming method (wheel vs. mold), and wall thickness can cause slightly different shrinkage in different directions, so for precise work it is best to verify with an actual test tile.

Where does the 12% shrinkage figure for stoneware come from?

It is a commonly cited approximate average for stoneware clay bodies. Actual shrinkage varies by manufacturer, so check your specific clay's technical data sheet if you need an exact figure.

Do I need to calculate drying shrinkage and firing shrinkage separately?

This calculator applies one combined "total shrinkage" figure covering both drying and firing. Most clay manufacturers also publish a single total shrinkage number, so you can enter that value directly.