Clay Shrinkage Calculator

Clay shrinkage is the reduction in size that occurs as clay dries and is fired. As water evaporates from the clay body, the particles compact together, causing the piece to become smaller than its original wet dimensions. This shrinkage is unavoidable and must be accounted for when designing pottery or sculpted pieces.

The formula is simple: Final Dimension = Original Dimension × (1 − Shrinkage% / 100). For example, if your clay has a 12% shrinkage rate and your original length is 20 cm, the final length will be 20 × (1 − 0.12) = 17.6 cm. This calculator applies that formula to all three dimensions automatically.

Multiply each original dimension by (1 − 14/100) = 0.86. So a piece that is 10 cm long will shrink to 10 × 0.86 = 8.6 cm. Enter 14 in the Shrinkage Rate field of this calculator and it will do the math for you across all dimensions.

Most standard pottery clays shrink between 8% and 15% from wet to fired state. Earthenware typically shrinks around 8–10%, stoneware around 10–13%, and porcelain up to 12–15%. Metal clays like fine silver or copper art clay can shrink significantly more — often 15–30% depending on the brand.

Metal clay is a crafting material made from tiny metal particles (such as silver, gold, copper, or bronze) mixed with an organic binder and water. When fired, the binder burns away and the metal particles sinter together, causing significant shrinkage. Fine silver metal clay typically shrinks about 8–30% depending on the brand, while copper and bronze clays shrink around 15–25%.

Divide your desired final dimension by (1 − Shrinkage% / 100) to find the starting size you need. For example, if you want a finished piece that is 10 cm and your clay shrinks 12%, you need to start with 10 / 0.88 ≈ 11.36 cm. This calculator shows you the final size from a given original size — work backwards from your target to find the right starting dimensions.

Grog (crushed, fired clay) is the most common material added to clay bodies to reduce shrinkage. It acts as a filler that doesn't shrink, reducing the overall shrinkage rate and improving the clay's structural stability during drying and firing. Sand and other non-plastic materials can also help reduce shrinkage.

In most cases, homogeneous clay bodies shrink roughly equally in all directions (isotropic shrinkage). However, if clay is heavily worked or thrown on a wheel, the alignment of clay particles can cause slightly different shrinkage rates in different directions. For practical purposes, applying the same shrinkage percentage to all dimensions gives a reliable estimate.