How thick should a silicone mould be?

Standard wall thickness is 10-20 mm for silicone moulds. Thin walls (10 mm) work for small, simple shapes. Complex forms with undercuts need 15-20 mm. Very large moulds may need 25 mm plus a rigid mother mould.

Why is silicone so expensive?

Silicone rubber costs £35-50 per kg in the UK. Its high price is offset by durability — a good silicone mould lasts 20-50 castings. Plaster moulds are cheap but limited to 1-5 uses. Consider cost per casting, not per mould.

What is the cheapest mould material?

Plaster of Paris is the cheapest at about £2/kg. It works well for simple shapes and waste moulds (broken off after one use). Jesmonite at £8/kg is good for larger piece moulds. Alginate (£25/kg) is for life casting.

How do I calculate an irregular object volume?

This calculator estimates volume as 70% of the bounding ellipsoid — a good average for organic sculpture shapes. For precise measurement, submerge the object in water and measure displacement.

Do I need a mother mould?

Flexible moulds (silicone, latex) need a rigid outer shell (mother mould) to maintain shape during casting. Make the mother mould from plaster bandage or fibreglass. Two-part mother moulds allow easy demoulding.

ArtCalcs

Mould Volume Calculator — Silicone & Plaster Moulds

Calculate the volume of silicone or plaster needed to make a mould.

Object Width

Object Height

Object Depth

Mould Wall Thickness

Mould Material

How We Calculate This

How Mould Volume Calculation Works

Mould material = Mould box volume - Object volume

The calculator computes the mould box volume (object + wall thickness on all sides) and subtracts the estimated object volume. Object volume is approximated at 70% of the bounding ellipsoid. Material weight and cost are derived from density and price per kilogram.

Frequently Asked Questions

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Last updated: February 2026

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