Clay Shrinkage Calculator — Pottery Fired Size
Enter your clay body's drying and firing shrinkage rates to find the final fired size from a wet measurement, or the wet size you must make to hit a target fired dimension.
I know the…
mm
%
%
Linear dimension after drying and firing
- 1
Dry retain factor
1 − 8 ÷ 100 = 0.92Fraction of linear size kept after drying. - 2
Fire retain factor
1 − 10 ÷ 100 = 0.9 - 3
Combined retain factor
0.92 × 0.9 = 0.828 - 4
Fired size
100 × 0.828 = 82.80
How does this calculator work?
Fired size = Green × (1−DS%) × (1−FS%). For 8% drying and 10% firing: retain factor = 0.92 × 0.90 = 0.828; a 100 mm wet piece fires to 82.8 mm. Reverse it: to get a 100 mm fired piece, make it 100 ÷ 0.828 = 120.8 mm wet. Total linear shrinkage = 1 − (1−DS%)(1−FS%).
Formula
How this is calculated
Clay shrinks in two distinct stages. During drying (wet to bone-dry), water evaporates from the clay body and the particles pack closer together. The drying shrinkage rate is the percentage by which a linear dimension decreases in this stage — typically 5–8% for earthenware, 8–12% for stoneware, and 10–15% for porcelain. During firing, organic matter burns off and vitrification begins, causing further shrinkage — typically 5–8% for earthenware, 10–14% for stoneware, and 12–18% for porcelain.
Because both stages apply sequentially, the total shrinkage factor is their product: (1 − DS/100) × (1 − FS/100). A clay with 8% drying shrinkage and 10% firing shrinkage retains 0.92 × 0.90 = 0.828 of its original linear dimension — a total linear shrinkage of 17.2%. To convert to volumetric shrinkage, cube the linear factor: (0.828)³ ≈ 0.567, meaning the piece loses about 43% of its volume.
The entered shrinkage percentages are typical values for the clay body type but vary with specific clay formulation, moisture content, and kiln temperature. Always test-fire a sample tile with scribed lines to measure your actual clay's shrinkage before making work to precise dimensions.
Frequently asked questions
Scribe a 100 mm (or 10 cm) line on a freshly made test tile. Measure again after drying and again after firing. Drying shrinkage % = (100 − dried length) / 100 × 100. Firing shrinkage % = (dried length − fired length) / dried length × 100. Always test the specific clay body at your specific firing temperature.
Each shrinkage stage applies to the size already reduced by the previous stage — not to the original size. For 8% drying and 10% firing, the total is not 18% but 17.2%: (1−0.08)×(1−0.10) = 0.828. Adding percentages would over-estimate the total shrinkage.
For hand-built or thrown pieces it is approximately equal in all directions, so this linear formula applies to height, width, and diameter alike. Extruded or slab-rolled work often shrinks more in the throwing direction; consult your clay supplier's data sheet for anisotropic bodies.
Also known as
TG we-Calculate Editorial Team. (2026). Clay Shrinkage Calculator — Pottery Fired Size [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/clay-shrinkage-calculator
TG we-Calculate Editorial Team. "Clay Shrinkage Calculator — Pottery Fired Size." TG we-Calculate. 2026. https://we-calculate.com/calculator/clay-shrinkage-calculator.
TG we-Calculate Editorial Team, "Clay Shrinkage Calculator — Pottery Fired Size," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/clay-shrinkage-calculator
@misc{wecalculate_clay_shrinkage_calculator, title = {Clay Shrinkage Calculator — Pottery Fired Size}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/clay-shrinkage-calculator}}, year = {2026}, note = {TG we-Calculate} }
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