Plaster Calculator
Calculate plaster or render quantities for walls and ceilings.
Please note: Material estimates for planning only. Always confirm quantities against your drawings, local building codes and supplier specifications before ordering. Structural work requires a qualified engineer.
What the Plaster Calculator does
Plaster volume is area times thickness. Because it is applied thin over a large area, small thickness changes move the material quantity a lot — going from 12 mm to 15 mm adds 25% to the cement bill.
Formula
Wet volume = Area × ThicknessDry volume = Wet volume × (1 + Waste %) × 1.3Cement = Dry volume ÷ Total parts × 1,440 kg/m³
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Area to plaster | m² | Yes | Accepts more than 0. |
| Plaster thickness | mm | Yes | Accepts 1 or more. |
| Mix (cement : sand) | one of 3 options | Yes | — |
| Cement bag size | kg | Yes | Accepts 1 or more. |
| Waste allowance | % | Yes | — |
How to use it
- Choose Mix (cement : sand).
- Enter Area to plaster, Plaster thickness, Cement bag size and Waste allowance.
- Select Calculate.
Worked example
40 m² at 12 mm with a 1:5 mix, 20% waste, 50 kg bags.
- Area
- 40
- Thickness
- 12
- Mix
- 1:5
- Waste
- 20
Wet 0.48 m³, with waste 0.576 m³, dry 0.749 m³ → cement 0.125 m³ = 180 kg = 4 bags, sand 0.624 m³.
Frequently asked questions
How thick should plaster be?
12–15 mm for a two-coat internal system, 2–3 mm for a skim over plasterboard, and 15–20 mm for external render.