Paint Coverage Calculator
Work out how much paint is needed from the surface you actually intend to coat. Enter gross area, openings, manufacturer coverage, coats and a practical allowance to turn a coverage rate into a procurement quantity.
Surface and paint inputs
Paint requirement
How the paint coverage calculation works
Paint quantity begins with the area that will actually receive paint. Openings such as doors and windows can be deducted where they are genuinely outside the painting scope.
Net paint area = gross area − unpainted openings
Theoretical paint = net area × coats ÷ coverage
Planning quantity = theoretical paint × (1 + allowance)
Why coverage alone is not enough
A quoted spread rate describes an assumed application condition. Real coverage can change with substrate texture, porosity, colour, application tool, viscosity and the amount left in trays or equipment.
Worked example
For a 12 m × 3 m surface with 6 m² of openings, the net area is 30 m². At 10 m²/L and two coats, the theoretical quantity is 6 L. With an 8% allowance, the planning requirement is 6.48 L, so a 10 L container would cover the calculated requirement.
Why the number of coats should be explicit
One coat and two coats represent different material demands. Keeping coats separate also makes quotations easier to compare when different paint systems recommend different application schedules.
Practical procurement
Use this result as a takeoff baseline, then compare it with the manufacturer's technical sheet and the actual wall or floor condition. Keep a consistent coverage basis when comparing products.
Common paint-estimating mistakes
Typical errors include using gross wall area when openings are excluded, forgetting the second coat, mixing m²/L with L/m², and assuming the theoretical spread rate is the guaranteed site yield.
Frequently Asked Questions
Should coverage be entered per coat?
Yes, unless the manufacturer's documentation clearly defines it differently.
Can I deduct doors and windows?
Yes, where they will not be painted.
Why add an allowance?
To account for practical application and site losses.
Can I estimate paint cost?
Yes, using your own price per litre.