What is a clay shrinkage calculator?
Clay keeps shrinking as it goes through bisque firing and then glaze (final) firing, typically somewhere between 5-20% depending on the clay body. The Clay Shrinkage Calculator takes either your bisque-stage size or your finished final size — whichever you know — and calculates the other automatically using the formula "final size = bisque size × (1 − shrinkage rate)". Width, depth, and height can each be calculated in either direction, so you can preview what an already-bisqued piece will measure once fired, or work backward from a target final size to see how big it needs to be at the bisque stage.
How to use it
Enter your clay's shrinkage rate (%), or tap one of the common-rate preset buttons to select one quickly. Then enter whichever you know — bisque size or final size — into the width, depth, and height fields, and the other side fills in automatically. If both sides already have values and you edit one of them, the other recalculates based on your latest edit. Once width and height are available, two pottery silhouettes are drawn to scale so you can compare the sizes at a glance.
When it comes in handy
- Previewing what size an already-bisqued piece will end up after the final firing
- Working out how big to make something at the bisque stage to hit a target final size
- Recalculating sizes when switching to a new clay body with a different shrinkage rate
- Comparing bisque and final sizes at once for work where width, depth, and height all matter
Frequently Asked Questions
- Does this only account for shrinkage between bisque and final, or the whole process from wet clay?
- It applies your entered shrinkage rate (%) directly between the bisque size and the final size fields. If you know the total shrinkage rate from the wet/forming stage instead, you can enter your forming size into the bisque field and use it the same way.
- What happens if both sides already have values and I change one?
- The field you just edited becomes the new reference, and the opposite field recalculates and updates automatically.
- What's a typical clay shrinkage rate?
- It varies by clay body, but it's generally around 5-15%, with some kaolin-heavy or porcelain bodies shrinking as much as 15-20%. Check your clay manufacturer's spec sheet or run a test firing for the most accurate number.