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Pottery Clay Shrinkage Calculator

Calculate clay shrinkage percentage from wet, dry, and fired dimensions. Plan pottery sizes accurately for clay bodies from leather-hard through glaze firing.

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Inputs that matter
Wet (Thrown) Size, Drying Shrinkage, Firing Shrinkage
Output to expect
Clay Shrinkage Calculator
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Linear Shrinkage Percentage

Shrinkage is the percent change in length between two stages. Most studio measurements track wet-to-fired or dry-to-fired linear shrinkage on test bars.

Shrinkage (%) = ((L_start − L_end) / L_start) × 100

Stage-by-Stage Breakdown

Drying shrinkage occurs from wet to bone-dry as physical water leaves. Firing shrinkage occurs from bone-dry to mature temperature as particles vitrify and sinter.

Total shrinkage = drying shrinkage + firing shrinkage (approximate for small values)

Scaling Finished Dimensions

To make a fired piece of target dimension, divide the desired finished size by (1 − total shrinkage fraction) to find the wet or leather-hard forming size.

Wet size = Fired size / (1 − shrinkage%/100)

Updated: July 2026

Example Scenarios

Stoneware body with 12% total shrinkage needs a wet thrown height of 4 / 0.88 ≈ 4.55 inches. Trim foot when leather-hard accounting for ~2% drying shrinkage remaining.

Jar and lid thrown from the same body at 13% shrinkage: if the wet jar rim is 4.0 inches ID, fired ID ≈ 3.48 inches. Size the lid gallery accordingly at wet stage.

Cut a 10 cm wet bar, measure at wet (10.0 cm), dry (9.2 cm), and cone 6 fired (8.7 cm). Calculator yields 8% drying + 5.4% firing = 13% total linear shrinkage.

Common Mistakes to Avoid

Measuring only dry-to-fired shrinkage and ignoring drying shrinkage

If you form work at wet stage, you need total wet-to-fired shrinkage. Dry-to-fired alone underestimates how much larger to throw or build the piece.

Assuming all clay bodies shrink the same amount

Grog bodies shrink less than fine porcelain. Recalculate whenever you change clay supplier, body formula, or firing temperature.

FAQ

Stoneware and porcelain bodies commonly shrink 10–15% from wet to fired. Earthenware may shrink 8–12%. Always test your specific clay body rather than using generic values.

For homogeneous thrown or pressed clay, linear shrinkage is approximately equal in all directions. Extruded or heavily textured bodies may show slight anisotropy.

Mark and measure test bars at wet/leather-hard, bone-dry, and fired states. Use the same moisture stage consistently when scaling work — most potters scale from wet or leather-hard.

Yes. Underfired ware shrinks less and absorbs water. Overfiring increases shrinkage and can cause bloating. Record shrinkage at your standard maturity cone.

Glaze coats add negligible dimension compared to clay shrinkage. Fit matters more: a glaze under compression or tension can affect final size by fractions of a millimeter.

About Pottery Clay Shrinkage Calculator

Clay bodies shrink at every drying and firing stage. Measuring wet, bone-dry, and fired dimensions lets you calculate total and stage-specific shrinkage so thrown or handbuilt pieces finish at the intended size.