Home Improvement
Paint Quantity Calculator
Work out how much paint you need for your walls, including doors, windows, coats and allowance.
How much paint do I need?
Measure the length, width and wall height. The calculator estimates wall surface, subtracts openings, then applies coats, coverage and an allowance. Buy in the tin sizes your supplier actually sells — suggested litres are often rounded to common tin steps. Coverage varies by surface porosity, colour change and brand; check the tin rather than a generic chart. New plaster usually needs sealing and more coats than a similar-colour refresh. Related finishing quantifiers: tile calculator and flooring calculator. Textured walls and heavy rollers use more paint than smooth-wall charts suggest. Estimate only — not a decorator’s quote. Dark colours over light walls often need an extra coat beyond the tin’s optimistic chart. Buy all emulsion for a room from the same batch number when you can, and stir tins together for large areas. Ceiling paints and kitchen formulations differ — do not assume one coverage number fits every surface in the house.
Worked example
Room 4 m × 3.5 m, wall height 2.4 m. Gross wall area ≈ 2 × (4 + 3.5) × 2.4 = 36 m². Subtract a 2 m² window and 1.8 m² door → about 32.2 m². Two coats at 12 m²/L coverage suggests roughly 5.4 L before waste — often two 2.5 L tins plus a tester, or a 5 L and a spare 1 L depending on brand sizes.
Limits and assumptions
Assumes rectangular walls. Vaulted ceilings and stairwells need segmented areas. Does not specify primer type. Not advice on VOC regulations or listed-building constraints.
Frequently asked questions
How many coats should I assume?
Two is common over a similar colour; stark changes or new plaster may need a primer plus extra coats.
Should I paint ceilings in the same estimate?
Add ceiling area separately if the tool focuses on walls, or include it when the form asks for full room surfaces.
Why do I still run short?
Textured walls, dark colours and heavy rollers use more paint than smooth-wall coverage charts suggest.
Do sample pots count toward coverage?
Rarely — treat them as colour tests, not part of the main litre estimate.
How should I treat radiators and trim?
Estimate woodwork separately; gloss and eggshell coverages differ from emulsion.