Clay Shrinkage Calculator for Pottery

Make a test tile, mark a line of known length such as 10 cm on it while wet, then fire it to your usual cone and measure the line again. Shrinkage percent is the lost length divided by the original length, times 100.

Switch the menu to 'fired size' and enter the finished measurement you want. The tool divides by the shrinkage factor to give the wet size to build, so the piece lands on target after firing.

It is the multiplier from wet to fired, equal to 1 minus shrinkage over 100. At 12 percent shrinkage the factor is 0.88, so any wet length times 0.88 gives the fired length, and a fired length divided by 0.88 gives the wet length.

Yes. The same clay usually shrinks more at a higher cone as the body matures and vitrifies further. Measure your shrinkage at the cone you actually fire to, since a bisque figure will understate the total.

Yes. Shrinkage is a ratio, so the wet and fired sizes come out in whatever unit you type, whether millimeters, centimeters or inches. Just keep both measurements in the same unit.

No. It uses one total wet-to-fired shrinkage figure, which folds drying and firing together. That single number is what most clay suppliers publish and what a test tile measures from wet to finished.

Sizes are rounded to four decimal places, so a value like 8 divided by 0.87 shows as 9.1954. That precision keeps back-calculated wet sizes accurate enough to mark out on a piece.

For most clay it is close to uniform, so a diameter, a height and a wall length all shrink by about the same percent. Throwing and slab work can add slight directional differences, so treat the result as a close estimate.

Many stoneware and porcelain bodies land between 10 and 15 percent total, while some earthenware is lower. The tool defaults to 12 percent, but always confirm with a test tile in your own clay and kiln.