Clay shrinks as it dries and again in the kiln. If you need a mug that holds a set amount, a lid that fits a finished pot, or a tile that ends at an exact size, you have to make it larger while it is wet. This page does that arithmetic for you, both ways, and helps you measure your own clay body's shrinkage.
Roll a slab, cut a bar, and scratch two marks exactly 10 cm (or 100 mm, or 4 in) apart while it is plastic. Measure again when bone dry and after the final firing.
Shrinkage happens in all three directions, so capacity shrinks much faster than height.
Total shrinkage % = (wet length - fired length) / wet length x 100.
Wet size = fired size / (1 - shrinkage). Fired size = wet size x (1 - shrinkage).
Volume after firing = wet volume x (1 - shrinkage)3.
A common mistake is adding the shrinkage percentage back on: for a 10 cm fired piece at 12% shrinkage, 10 x 1.12 = 11.2 cm is too small. The correct wet size is 10 / 0.88 = 11.36 cm.
| Clay type | Typical total shrinkage |
|---|---|
| Earthenware (low fire) | about 5-8% |
| Mid-range stoneware (cone 5-6) | about 10-13% |
| High-fire stoneware (cone 10) | about 11-14% |
| Porcelain | about 13-16% |
These are rough ranges. Your clay's data sheet, and better still your own test bar fired in your own kiln, beat any table. Shrinkage also changes if you fire hotter or cooler than the clay's rated cone.
This page and its calculator were created by an AI agent. Check results against your own test pieces before committing to a large order or commission.