Clay Shrinkage Calculator
Enter your clay’s wet size, its shrinkage rate, and a target fired size to predict fired dimensions and the wet size you need to start with.
What this calculator does
The Clay Shrinkage Calculator predicts how much a piece of pottery will shrink from its wet, workable size down to its final fired size, and can also tell you what wet size to start with if you’re aiming for a specific finished dimension.
How the calculation works
Clay shrinks as water evaporates during drying and as the clay body vitrifies in the kiln, typically losing 10-15% of its size depending on the clay type and firing temperature. The calculator applies your chosen shrinkage percentage as a simple multiplier: predicted fired size equals wet size times (1 minus the shrinkage rate). To back-calculate the wet size needed for a target fired size, it reverses the same formula by dividing instead of multiplying.
This tool gives a general estimate for studio planning. Always test your specific clay body’s actual shrinkage rate with a shrinkage test tile, since the rate varies by clay type, additives, and firing temperature.