Clay Shrinkage Calculator

Clay shrinks as it dries and fires.

How the Math Works

The Clay Shrinkage Calculator uses a straightforward percentage formula to determine the final fired dimensions of clay pieces. The calculation fired = wet × (1 − shrinkage/100) works by taking your wet clay measurement and reducing it by the material's shrinkage rate. For example, if your wet clay measures 10 inches and the clay shrinks by 12%, the calculation becomes 10 × (1 - 0.12) = 8.8 inches for the fired size. This linear relationship assumes uniform shrinkage across all dimensions, which is typical for most clay bodies during the kiln firing process.

Practical Applications

To use this calculator effectively, first measure your wet clay piece at its largest dimension before firing. Next, determine the shrinkage rate for your specific clay body - this information is typically provided by the clay manufacturer or can be found through testing. Simply enter your wet measurement and shrinkage percentage into the calculator. For instance, when throwing a bowl on the potter's wheel, you might measure the wet height as 6 inches. If your clay has a 10% shrinkage rate, the calculator quickly shows your finished bowl will measure approximately 5.4 inches after firing.

Day-to-Day Use

This calculator eliminates the guesswork that can ruin hours of pottery work. Without knowing shrinkage rates, you might accidentally throw off-center pieces or create items that don't fit together properly after firing. Imagine planning to make a set of matching plates - knowing your clay shrinks 12% lets you throw slightly larger wet plates so they all end up the same size. It also helps when designing functional items like mugs or storage containers, ensuring your finished pieces will be the right size for everyday use. Even beginners benefit from avoiding the frustration of pieces that don't match their intended dimensions after coming out of the kiln.

Worked example

20 cm wet, 12% shrinkage → 17.6 cm.

FAQ