Stoneware clays shrink about 6% from web to bone dry. They shrink insignificantly in the bisque firing, and about 6% in a cone 10 glaze firing. Total shrinkage from wet to glaze fired is therefore about 12% when working at cone 10. Different clays shrink somewhat more or less. A lower glaze firing temperature will produce a lower shrinkage rate. Your piece may shrink more in one direction than another direction also.
For instance, a thrown cylinder may shrink a greater percentage in its diameter than in its height. A rolled slab may shrink a greater percentage in the rolled direction than in its width.
A little experimenting with the Creative Industries Shrink Rule will quickly give you a high degree of accuracy in predicting shrinkage in your particular clay, in your studio, using your techniques.
1. If you want a piece to measure 8" after a 12% shrinkage, use the 12% scale on your Shrink Rule to measure 8" on the wet clay.
2. To make a replacement lid for a casserole which has been bisqued, measure the casserole with a regular ruler. Use this same measurement on the wet clay using the 6% scale on your Shrink Rule.
3. Your friend just broke her teapot lid. You have lots of teapot lids which have been bisqued, but which one, after its glaze firing will fit your friends teapot? Measure the teapot with a regular ruler. Now find the bisque lid with the same measurement using the 6% scale on your Shrink Rule.