How do I find the volume of my mould?

Fill the mould with water and pour it into a measuring jug. The volume in ml equals cm³. For sealed moulds, weigh the water (1 ml = 1 g). The Mould Volume Calculator can also estimate this from object dimensions.

Which casting material is cheapest?

Plaster is the cheapest casting material (£2/kg). Concrete is also very cheap. Jesmonite (£8/kg) offers a good balance of cost and quality. Polyester resin (£10-15/kg) and polyurethane (£15-20/kg) are mid-range. Epoxy is most expensive (£20-40/kg).

Why add 15% for waste?

Casting wastes material through mixing residue in containers, overflow, test pours and trimming. Resin especially requires accurate mixing — excess is always better than too little. 15% is a conservative allowance.

Can I mix different casting materials?

Never mix different resin types. You can add fillers to most casting materials: stone powder, metal powder, pigment, sand, sawdust. Fillers can change the appearance, weight and cure time. Test small batches first.

What safety precautions do I need?

Wear nitrile gloves, safety glasses and use adequate ventilation for all resins. Polyester resin produces styrene fumes — use outdoors or with extraction. Epoxy can cause skin sensitisation. Always read the SDS (Safety Data Sheet).

ArtCalcs

Casting Calculator — Resin, Plaster & Concrete

Calculate resin, plaster or concrete volume and weight for casting.

Volume per Cast

Fill mould with water to measure

Number of Casts

Casting Material

Cost per kg (optional)

How We Calculate This

How Casting Calculation Works

Material weight = Volume x Density x Number of casts x 1.15 waste

The volume of each cast is multiplied by the material density to get weight per cast. This is multiplied by the number of casts and a 15% waste factor. Cost is calculated from the total weight and your price per kilogram.

Frequently Asked Questions

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Last updated: February 2026

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