Shrinkage Rate Calculator

Clay shrinks twice on its way from a freshly-formed piece to a finished one: once as the water evaporates out while it dries to "bone-dry," and again as the clay body vitrifies in the kiln. This calculator chains those two shrinkage stages together. Wet Size is your piece's measurement the moment it's formed, still full of water. Wet-to-Dry Shrinkage is the percentage the clay loses going from wet to bone-dry -- typically 4-8% depending on the clay body, mostly from water leaving the clay structure. Bone-Dry Size applies that first percentage to Wet Size.

Dry-to-Fired Shrinkage is the second, separate percentage lost during firing, as the clay particles fuse and any remaining structural water and organics burn off -- also typically 4-8%, and it tends to run higher at higher firing (cone) temperatures, since a hotter fire vitrifies the clay body more completely. Final Fired Size applies that second percentage on top of the already-shrunk Bone-Dry Size, not on the original Wet Size, since the two shrinkage stages happen sequentially rather than in parallel -- this compounding is why total shrinkage across both stages is always a bit more than the sum of the two percentages alone (two 6% shrinkages compound to about 11.6% total, not 12%). Total Shrinkage reports that compounded percentage and the actual size lost between Wet Size and Final Fired Size. Wet Size to Hit This Final answers the reverse question: if you need a specific finished dimension out of the kiln, what wet size should you start with, given the same two shrinkage percentages -- essential for mold-making and any project with a hard dimensional target. Every clay body shrinks differently, so run a test tile through your own wet-to-fired process and measure it before trusting these percentages for a project where the final size really matters.