Clay & Shrinkage

Target Finished Size Calculator

Calculate the wet throwing size needed to achieve a specific finished fired dimension.

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Results

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Enter your measurements above and click Calculate.

Formula Explanation

To achieve a specific fired dimension, you must throw (or build) the piece larger to account for clay shrinkage. ClayCalc also applies a +0.2% empirical re-hydration correction factor observed in studio practice.

Wet Size = Final Size ÷ (1 − shrinkage% ÷ 100)

Common Mistakes

  • cancel Using an inaccurate shrinkage rate. The result is only as good as your shrinkage data. Always test your specific clay body and firing cone — don't rely solely on the manufacturer's stated shrinkage.
  • cancel Applying one shrinkage rate to all directions. For functional lids and galleries, measure shrinkage in both the horizontal and vertical axes separately.

Frequently Asked Questions

Why does the wet size include a correction factor? expand_more
ClayCalc applies a +0.2% empirical re-hydration correction to account for slight clay re-absorption during forming, which is commonly observed in studio practice.
Can I use this for slab work as well? expand_more
Yes. Enter the desired finished slab dimension and apply your clay body's total shrinkage rate. For directional work, calculate horizontal and vertical axes separately if your clay shows anisotropic shrinkage.
Should I throw bigger or smaller for lids? expand_more
Always throw lids slightly larger than the calculated wet size (add 2–3mm) to allow for final fitting by sanding or trimming after firing.