About this calculator
How many bags of plaster or render a wall needs, for skim, two-coat and render systems.
How it’s calculated
Coverage per 25 kg bag used: multi-finish about 10 m² at 2 mm, bonding about 2.75 m² at 8 mm, hardwall about 3.4 m² at 11 mm. Render is worked out by volume at 20 mm, using a dry-volume factor of 1.3.
Worked example
With these inputs:
- Wall length
- 4 m
- Wall height
- 2.4 m
- Openings to subtract
- 0 m²
- System
- Skim coat, 2 mm (multi-finish)
- Waste allowance
- 10%
the result is:
- Bags needed
- 2 × Multi-finish, 25 kg
- Area (incl. waste)
- 10.56 m²
- System
- Skim coat, 2 mm (multi-finish)
Tips from the trade
- Uneven or chased walls eat more undercoat. Add 10–20%.
- Check the suction of the background before choosing an undercoat.
Common questions
How much does a bag of multi-finish cover?
About 10 m² at 2 mm, sometimes 9–11 m² depending on the plasterer.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the Building Regulations before ordering.