How to calculate how much paint you need
Measure the perimeter, subtract openings and use the coverage stated for your paint. The allowance and pack rounding are shown separately.
- Measure length, width and height.
- Subtract openings and check coverage.
- Choose coats, allowance and tin size.
Formula
Net wall area = 2 × (length + width) × height − openings. Add length × width if including the ceiling. Litres = area × coats ÷ coverage × (1 + allowance/100).
A 4 × 3 m room
With a height of 2.5 m and 3 m² of openings, the net wall area is 32 m². Two coats at 10 m²/L need 6.4 L. Adding 10% gives 7.04 L: 3 tins of 2.5 L, or 7.5 L purchased.
- The room is approximated as a rectangle.
- Coverage is for one coat on the intended surface.
- Primer, moisture and texture effects are not calculated automatically.
Frequently asked questions
Should I subtract doors and windows?
Enter their combined area if they will not receive this paint. Do not subtract the same opening twice.
Does the ceiling use the same paint?
Include it only when product, coverage and coats match. Otherwise calculate the ceiling separately.
Why do I buy more litres than the estimate?
The number of tins is rounded up to a whole number. This difference is separate from your chosen allowance.