Plaster quantity calculator
Wall area and plaster thickness in, cement and sand out — for internal or external work, one face or both, at whatever mix ratio your specification calls for.
Wet volume = Net area × Thickness
Area — ft² · sand — cft (— kg) · wastage is applied to cement and sand, not to area
How this calculator works
- Net area = wall area × the number of faces, less the openings you enter.
- Wet volume = net area × thickness. A 12 mm coat on 30 m² is only 0.36 m³ — plaster quantities are small, which is why percentage wastage matters so much here.
- Dry volume = wet volume × 1.27, then split by the mix ratio into cement and sand.
- Wastage is applied to the materials rather than the area, because most plaster waste is dropped mortar rather than over-coverage.
Fifteen per cent wastage is a realistic default for hand-applied plaster and is deliberately higher than the 3–5% used for concrete. Mortar falls off the wall, sets in the pan, and gets left in the mixer.
Thickness is the other lever. External plaster at 20 mm uses two-thirds more material than internal at 12 mm for the same wall, so check which you are pricing before ordering.
Read the full guide: Cement, Sand & Aggregate for M20: Quantities per Cubic Metre
No signal at the site? Take this calculation offline.
Every calculation a site needs — concrete, brick, steel, plaster, paint and more — in one app that works offline, in metric and imperial, anywhere in the world.
