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Paint Calculator — Walls, Ceilings & Coats
Work out paint for one rectangular room, with separate wall and ceiling quantities. Deduct doors and windows, choose each paint’s coverage and number of coats, then round up to whole tins.
Coverage must be per coat. Use the value on your chosen paint and adjust for your surface. Defaults and prices are examples; primer, trim, labour and tax are not included. Changing units changes how the entered numbers are interpreted.
How much paint do I need?
Wall area is 2 × (room length + room width) × height, less doors and windows. Multiply this by the number of coats and divide by coverage per coat. Add your chosen allowance. Ceiling area is length × width and is calculated separately.
Worked example: a 5 × 4 m room with 2.5 m walls has 45 m² of wall area. Deducting 4 m² gives 41 m². At two coats, 10 m²/L coverage and 10% extra, walls need 9.02 L: four 2.5 L tins. The 20 m² ceiling needs 4.4 L: two 2.5 L tins. Example purchase cost is 140 in the selected currency.
Is the coverage on the tin for one or two coats?
Read the product instructions. Enter coverage for one coat here, then enter the required coats separately. Do not use a two-coat coverage figure and also multiply by two.
Can I exclude the ceiling?
Yes. Set ceiling coats to 0. The ceiling quantity and tin count will both be zero. Keep the other ceiling fields at valid positive example values.
Should I always deduct doors and windows?
This tool lets you deduct their total measured area. Enter 0 if you prefer to keep that area as additional allowance. Do not deduct the same opening twice.
Why might actual coverage be lower?
Porosity, texture, colour changes, application method and product choice can affect coverage. Use a sample patch and the paint manufacturer’s advice. An allowance cannot guarantee enough paint for every surface.
Sources and assumptions
Method and product-dependent coats: Dulux paint calculation guide and Dulux paint calculator. No brand-specific coverage is assumed. Reviewed 30 October 2026. Calculations run in your browser; this calculator does not send your entered measurements to a server.
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