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 tool runs entirely in your browser. Your files are never uploaded to a server.
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.