Plaster coat Calculator: measuring notes and method
Use applied thickness
Measure net area and use the specified average applied thickness for that coat. Treat areas with substantially deeper fill separately; a thin finish coat over the whole wall does not account for local repairs.
Compare with product bag coverage
The density input must represent material consumption per applied volume. Where the manufacturer gives area per bag at a stated thickness, use that yield to check the bag estimate directly.
Formula
Mass = area × applied thickness × density × (1 + waste ÷ 100). Bags = mass ÷ bag size, rounded up.
Product reference: USG material estimator
Worked examples in metric and imperial units
Illustrative values match Reset example and stay fixed when you edit the calculator. Both columns describe the same calculation; converted inputs are rounded.
Metric worked example
- Total surface area
- 24 m²
- Applied thickness
- 10 mm
- Material density
- 1,600 kg/m³
- Bag size
- 20 kg
- Waste allowance
- 10 %
Bags to buy: 22
Imperial worked example
- Total surface area
- 258.3339 ft²
- Applied thickness
- 0.3937 in
- Material density
- 99.8847 lb/ft³
- Bag size
- 44.0925 lb
- Waste allowance
- 10 %
Bags to buy: 22
Follow the calculation
Lengths in this working are in metres.
- Applied volume including allowance = 24 × 0.01 × 1.1 = 0.264 m³.
- Material mass = 0.264 × 1,600 = 422.4 kg.
- Divide by 20 kg per bag and round up.
Reviewed 19 October 2026. How calculations are checked · Report a correction