Online Tool Store
Pottery Shrinkage Calculator
Enter your wet clay dimensions and your clay body's shrinkage percentage to calculate the final size after drying and firing.
This works right here on your device — nothing gets sent out.
Total shrinkage
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How it works
- Choose "Find shrinkage %" if you have both a wet/bone-dry and a fired measurement, or "Predict fired size" if you know your clay's shrinkage rate and want to know what size to start at.
- Enter your measurements or select a clay body preset for a typical shrinkage percentage.
- The result updates instantly as you type.
The formula
Shrinkage % = (Wet size − Fired size) ÷ Wet size × 100
Wet size to build at = Desired fired size ÷ (1 − Shrinkage % ÷ 100)
Example: a piece measuring 120 mm wet and 106 mm fired shrank (120−106)/120 × 100 ≈ 11.67%. To get a 150 mm fired piece at that same rate, build it at 150 ÷ (1 − 0.1167) ≈ 169.9 mm.
FAQ
What's the difference between the two modes?
"Find shrinkage %" works backward from two measurements you already have (wet/bone-dry and fired) to tell you your clay's actual shrinkage rate. "Predict fired size" works forward — given a known shrinkage rate and the fired size you want, it tells you what size to build or throw the piece at.
Why do the clay presets give a range instead of one number?
Shrinkage varies by specific clay body, firing temperature (cone), and even the individual batch, so manufacturer-published ranges (e.g. stoneware around 10–12%) are a starting point. For a piece where size accuracy matters, measure your own test tile through bisque and glaze firing and use "Find shrinkage %" with your real numbers instead of a preset.
Does shrinkage happen all at once?
No — clay shrinks in two stages: drying (wet to bone-dry) and firing (bone-dry to fired), and this calculator's "total shrinkage" figure covers the whole journey from wet to fired if you measure both endpoints, or from bone-dry to fired if that's what you measured.
How we compare
| Feature | Online Tool Store | Studio's printed shrinkage chart | Doing the math by hand |
|---|---|---|---|
| Works both directions (find % or predict size) | ✓ | ✗ | ✓ |
| Built-in clay body presets | ✓ | ✓ | ✗ |
| Free, instant | ✓ | ✓ | ✓ |
A shrinkage chart on the studio wall gives you a preset percentage; this also works the calculation backward from your own test tile measurements, and does the wet-size math for you either way.