Pottery Calculators

Clay quantities, shrinkage, glaze recipes, kiln loads and firing costs. 15 calculators for the wheel and the kiln.

Shrinkage is the number that decides whether a piece fits its purpose, and it catches beginners on every commission. Clay shrinks twice: once drying, once firing, and the total runs roughly 10 to 15% depending on the body. A mug thrown to hold exactly 350 ml wet will not hold it fired. Worse, the shrinkage compounds in three dimensions, so a 12% linear shrinkage is about 32% by volume. Anyone throwing to a specification, a lid that must fit a jar, a tile that must meet a grid, needs the wet dimension worked backwards rather than forwards.

Kiln electricity takes your tariff rather than assuming one, and the figures surprise people either way. A cone 6 firing in a mid-size electric kiln might use 30 to 60 kWh, so the cost of a firing swings by a factor of four between countries. Studio hire rates are often quoted per firing without that context.

Glaze recipe pages work in percentages by dry weight, the standard notation, and total to 100 before colourants. Colourants are added on top, which is why a recipe can total 104%.