Pottery Clay Weight Calculator
Work out how much clay to weigh out for a thrown cylinder or bowl from its height, diameter and wall thickness — before and after firing shrinkage.
How it works
Wet size = finished ÷ (1 − shrinkage) · Wall volume = π(r_out² − r_in²) × (h − base) · Base volume = π r_out² × base · Clay = volume × density
A thrown pot is a hollow cylinder: its clay volume is the walls (the ring between the outer and inner radius) plus the disc of the base. Because clay shrinks as water leaves during drying and firing, the piece you throw must be larger than the finished dimensions by the shrinkage factor, so every dimension is scaled up by 1 ÷ (1 − shrinkage). Multiplying the wet volume by the clay body density gives the ball of clay to centre. Real throwing wastes a little to trimming and the slurry lost while shaping, so round up.
Worked example
For a finished 12 cm diameter, 12 cm tall cylinder with 0.6 cm walls and a 1 cm base at 12% shrinkage, wet dimensions scale by 1 ÷ 0.88 ≈ 1.136 to about 13.6 cm ⌀ × 13.6 cm. The walls hold roughly 290 cm³ and the base about 165 cm³, so ~455 cm³; at 1.9 g/cm³ that is about 865 g of clay.
Frequently asked questions
How much shrinkage should I assume?
It depends on the clay body and firing temperature — most stoneware and porcelain shrink 10–15% total from wet to fired. Your clay supplier lists the figure, or you can measure a test bar before and after firing.
Why weigh clay before throwing?
Centering a consistent ball of clay makes forms repeatable and stops you running short mid-pull. Production potters weigh out identical balls so a set of mugs or bowls matches.
Does this include trimming waste?
No — it is the clay that ends up in the finished walls and base. Add roughly 15–25% if you trim a foot ring or throw with extra clay to open and pull comfortably.
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This calculator is for educational purposes. Double-check important results before acting on them.