How the math works
Pottery shrinkage is usually quoted as a linear percentage: how much a length
changes from wet to fired. If a clay shrinks 12%, a 10 cm fired diameter needs about
11.4 cm wet (fired / (1 - rate)). Going the other way:
wet × (1 - rate).
Volume shrinks more than length. At 12% linear, volume drops by roughly 32%, which matters for lids, fitted forms, and matching sets.
Why it matters
A mug that fits a lid or a set of bowls that stack depends on shrinkage. Measure once, convert with your clay's rate, and you skip a round of remakes.
Pro tip
Bag rates are a starting point. Measure a test tile wet and after firing, then use that custom rate here, or save it on the clay body in the Claybook app for every future conversion.