How to use this calculator
Add paintable wall areas and subtract large doors or windows. Include the ceiling only when using the same paint.
Surface texture, porosity and colour changes affect coverage. Check the product label and consider keeping paint from the same batch for touch-ups.
The formula
Litres = area × coats ÷ coverage × (1 + allowance ÷ 100). Tins = litres ÷ tin size, rounded up.
A worked example
40 m² with two coats at 10 m²/L and 10% extra requires 8.8 L. Four 2.5 L tins supply 10 L.
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