Litres of paint for a room, from its walls, the coats and the tin coverage rate
Runs in your browser. Nothing you type is sent anywhere. Updated on 24 Oct 2026.Paint Calculator turns a room into litres. A 12 by 10 foot room 10 feet high, less 40 square feet of doors and windows, needs 7.9 litres for two coats at 10 square metres a litre. Coverage, coats, wastage and the primer are all yours to set from the tin in front of you.
Under "Measure by", choose "Room size" or "Wall area", and pick Feet or Metres under "Measured in".
Enter the "Length", "Width" and "Wall height", or the "Surface to paint", and the "Doors and windows to deduct".
Pick a coverage chip for your paint type, or type the rate on the tin into "Coverage per litre, per coat", and set "Coats".
Set "Primer coats", "Wastage" and, if you want a cost, "Price per litre (optional)".
Read the "Paint needed" and "Tins to buy", then press "Share result" to copy a link.
The whole answer rests on one number, and it is printed on the tin rather than on this page: how many square metres one litre covers in one coat.
A smooth interior wall finished with putty takes around 10 square metres a litre of emulsion. Rough plaster takes closer to 7. A textured exterior wall can be down at 6. Acrylic distemper sits near 8, and enamel on smooth wood or metal stretches to 12. Those are the middles of the ranges manufacturers publish, and manufacturers do not agree with each other. So coverage is a box here, with those named starting points offered and the tin's own figure always the better one to use.
The rest is geometry. Wall area is twice the length plus the width, times the height. The ceiling is added if you are painting it. Doors, windows and a wardrobe front come off as a deduction. Multiply by the number of coats, divide by coverage, add a little wastage for the roller and the tray, and you have litres.
Primer is worked out on its own, because it has its own coverage and usually its own single coat, and because a repaint over sound paint needs none of it.
Litres alone are hard to shop with, so the page also suggests tins: 20, 10, 4 and 1 litre, largest first, never leaving you short.
Two honest limits. A first coat on bare plaster covers less than the coats after it, so a fresh wall will drink more than this predicts, and the wastage box is where that goes. And a strong colour change may need a third coat no calculator can foresee.
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About 7.9 litres for two coats, assuming 10 foot walls, 40 square feet of doors and windows deducted, and a coverage of 10 square metres a litre. That is 400 square feet of wall, painted twice, plus five per cent for the roller and the tray.
Around 10 for interior emulsion on a smooth putty wall, 7 on rough plaster, 6 on a textured exterior and 12 for enamel on smooth wood. Every manufacturer prints its own spreading rate on the tin, and that figure beats any default, which is why the box is editable.
Only if you are painting it, and often the ceiling takes a different paint anyway. The switch on this page adds length times width to the surface when you turn it on. Ceiling paint is usually a flat white emulsion with its own coverage, so it is worth a second run.
Two is the normal specification for emulsion over a primed wall, and it is what this page assumes. One coat is sometimes enough on a repaint in the same colour. A large colour change, particularly going light over dark, can need three, and no calculator can predict that from dimensions.
Usually one coat on new plaster and none at all on sound existing paint. The primer section on this page has its own coverage box because primers spread differently from topcoats, and for the example room a single primer coat at 10 square metres a litre works out at 4 litres.
Because 7.9 litres is not something a shop sells. The suggestion combines 20, 10, 4 and 1 litre packs, largest first, and never rounds down. Buying the larger tin is usually cheaper per litre, and a part-used tin is what you want for touching up afterwards anyway.
Formula only: no rates or limits are read from an official source.
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