Runs in your browser · nothing is uploaded
Paint Calculator
Measure the room or each wall, leave out doors and windows, and see how much paint and which tins you need — with primer worked out separately.
An estimate. Textured, porous or dark surfaces, strong colour changes and rollers versus sprayers all change how far paint goes.
How it's calculated
- Wall area2 × (length + width) × height − doors and windows
- Paintarea × coats ÷ coverage × (1 + extra %)
Worked example
100 m² of wall at 10 m² per litre: one coat is 100 ÷ 10 = 10 litres, two coats 20 litres. With 10% extra that's 22 litres — for example four 5 L tins and one 2.5 L tin.
Frequently asked questions
How much paint do I need for a room?+
Measure the wall area (room perimeter × wall height), subtract doors and windows, multiply by the number of coats and divide by the coverage on the tin. 100 m² at 10 m² per litre needs 10 litres for one coat and 20 litres for two, before any extra.
What coverage should I use?+
The figure printed on the tin. Many wall paints quote around 10–13 m² per litre or 350–400 ft² per US gallon, but rough, porous or dark surfaces and big colour changes use more.
Is a gallon the same everywhere?+
No. A US gallon is 3.785 litres and an imperial (UK) gallon is 4.546 litres. Pick the one your tins and coverage figures use.
Do I need primer?+
Usually on new plaster, bare wood or metal, stains, and when covering a much darker colour. Primer is a different product, so the calculator works it out separately.
Should I subtract doors and windows?+
Yes, for anything you won't paint. The calculator stops you if the openings come to more than the wall area rather than showing negative paint.
Which tins should I buy?+
Enter the sizes you can buy and, optionally, their prices. The calculator finds the cheapest whole-tin mix that covers what you need, or — without prices — the fewest tins that leave less than one small tin spare.