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?

Earthenware shrinks about 8%, stoneware 12%, and porcelain 15% from wet to fired. Shrinkage happens in two stages: drying (5-7%) and firing (3-8%). Always account for shrinkage when planning piece dimensions.

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 Type

Width / Diameter

Height

Depth (box only)

For box shape; ignore for others

Wall Thickness

0 for solid form

How We Calculate This

How Clay Weight Calculation Works

Weight = Clay volume x Density

The calculator computes the volume of your chosen shape, subtracts the hollow interior if specified, then multiplies by the clay density. Wet, dry and fired weights differ because water evaporates during drying and the clay body vitrifies during firing.

Frequently Asked Questions

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Last updated: February 2026

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