Paint Calculator
See how many litres of paint your job needs — from the wall area, the number of coats, and the coverage on the tin.
Two coats by default
Most interior walls take two coats for a solid, even finish — the calculator multiplies your wall area by the number of coats.
Coverage varies
Coverage depends on the paint and the surface. Always check the figure on your tin rather than assuming a fixed number.
How much paint do I need?
Wall area, coats, and coverage
A paint calculator turns three simple measurements into a litre figure you can take to the shop. You enter the total wall area you want to paint, how many coats you plan to apply, and how far one litre of your paint stretches — its coverage. From those it works out the total area to cover and the litres of paint that area needs, so you buy enough without lugging home half-empty tins.
First the calculator finds the total area to cover by multiplying the wall area by the number of coats. Then it divides that by the paint's coverage per litre to get the litres you need.
Litres = (wall area × coats) ÷ coverage per litreThe total area to cover is shown alongside the litres so you can see both the surface being painted (80 m² here, across two coats) and the paint that surface needs. Coverage of 11 m² per litre is a typical figure for interior emulsion, but the exact number is printed on your tin.
Suppose you are repainting a room with 40 m² of wall, two coats, and emulsion that covers 11 m² per litre.
Find the total area
40 m² × 2 coats = 80 m² to cover.Divide by coverage
80 ÷ 11 = 7.27 litres.Round up to buy
Buy a 7.5 L tin, or a 5 L plus a 2.5 L, with a little to spare.
The litres figure is the bare amount the maths calls for, so round up and buy a little extra — paint is wasted on roller trays and touch-ups, and matching a second batch later is hard. If your wall has large windows, patio doors, or full-height glazing, subtract their area from the wall area before you calculate so you do not significantly over-buy. Remember the result is for the topcoat only: if you are covering a much darker or lighter colour, or painting bare plaster, budget a separate primer or undercoat on top of this figure.
The arithmetic is exact, but real-world coverage is not.
Coverage depends on the surface and paint
The coverage figure assumes a smooth, sealed, similarly coloured surface. Porous, textured, or bare walls drink up more paint, so one litre covers less than the tin states and you will need more than the calculator suggests. Treat the result as a starting estimate, lean towards the higher tin size, and check the manufacturer's coverage for your specific paint and surface.