Shrinkage is how much clay gets smaller as it dries and fires, given as a percentage of its wet size. Most stoneware shrinks about 10 to 14% in total, roughly half in drying and half in the firing.
What Is Shrinkage?
As water leaves clay, the particles draw closer together and the clay shrinks. When it fires, more shrinkage follows as the particles fuse and pores close. Clay data sheets list drying shrinkage and total, or fired, shrinkage at specific cones, and the figures vary a lot between bodies.
Shrinkage matters whenever size matters: mugs that hold a set amount, lids that fit, tiles that line up, or sets that match. You make the wet piece larger than the finished size by dividing the target size by one minus the shrinkage, so a 10 cm finished piece at 12% shrinkage needs to be about 11.4 cm wet.
It also drives many faults. Parts that shrink by different amounts crack where they join, and pieces that dry unevenly warp or crack. Mixing clay bodies with different shrinkage in one piece is a common cause of trouble.
The best way to know your clay’s shrinkage is to measure it: mark a line of known length on a wet test bar, then measure it again after drying and firing.
This pottery glossary entry from Le Studio Art Space is general educational content. Always follow the clay, glaze and kiln makers’ data for your own materials and equipment.