How much does wet clay weigh?

Wet clay weighs about 1.7-1.9 g/cm³ depending on type. Stoneware is heavier than earthenware. A 20 cm solid sphere of stoneware weighs about 8 kg wet. Hollow forms use significantly less clay.

How much does clay shrink?

Total linear shrinkage from wet to fired is roughly 6-8% for earthenware, 11-13% for stoneware and 12-16% for porcelain. It happens in two stages — drying then firing — with each contributing about half. Because it is linear, a 12% rate means a piece loses around 32% of its volume, so always scale your dimensions up when planning a finished size.

Why should I hollow out large sculptures?

Solid clay pieces over about 3 cm thick can crack or explode during firing as trapped moisture turns to steam. Hollowing to 1-2 cm wall thickness reduces weight and prevents kiln disasters.

How thick should walls be for a hollow sculpture?

For most kilned work, walls should be 10-15 mm. Very large pieces can go to 20 mm. Thin walls (under 8 mm) may crack or warp. Air-dry clay can be thinner (5-8 mm) since it is not fired.

How do I buy the right amount of clay?

Buy 20-30% more than calculated to account for waste, test tiles and mistakes. Clay is sold in 10-12.5 kg bags in the UK. For a first project, start with one bag and track your usage.

ArtCalcs

Clay Weight Calculator — Solid & Hollow Sculpture

Estimate the weight of clay needed for a solid or hollow sculpture.

Shape

Clay TypeSelect a preset or enter custom density and shrinkage

Width / Diameter

Overall outside diameter or width (widest point)

Height

Overall height (not needed for a sphere)

Depth (box only)

Front-to-back size for a box; ignored for round shapes

Wall Thickness

Leave 0 for a solid form; 10-15 mm typical for hollow kiln work

How We Calculate This

How Clay Weight Calculation Works

Wet weight = Clay volume × wet density

The calculator works out the volume of your chosen shape from its outside dimensions, subtracts the hollow interior when you give a wall thickness, then multiplies by the wet plastic density to get the wet weight.

The bone-dry weight is the wet weight minus the water of plasticity (about 20% of the mass for a plastic clay body), since drying only removes water. The fired weight takes the shrunk fired volume — the clay volume reduced by the linear shrinkage in all three dimensions — at the higher vitrified density, giving a total wet-to-fired loss of roughly 20%.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify quantities before purchasing materials.