ArtCalcs.uk
Casting Calculator — Resin, Plaster & Concrete
Calculate resin, plaster or concrete volume and weight for casting.
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.
Densities are cured/set figures: Jesmonite AC100 1.75 g/cm³ (1,750 g per litre, per the manufacturer), concrete 2.3 g/cm³, plaster 1.6 g/cm³, and resins 1.1-1.2 g/cm³. Plaster varies from about 1.5 g/cm³ for a wet, open hand-pour up to 1.7 g/cm³ for a dense, low-water-ratio cast — this calculator uses 1.6 g/cm³, so expect ±5% on the plaster weight.
Frequently Asked Questions
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.
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).
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.
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.
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).
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Last updated: February 2026
All calculations are estimates. Always verify quantities before purchasing materials.