Plot No. 62 · Home & Garden
Paint Calculator
Work out how much paint a room needs. It measures the wall area as 2 times length plus width, times height, subtracts roughly 1.8 square metres for each door or window, then multiplies by the number of coats and divides by the paint coverage per litre.
Each opening is treated as roughly 1.8 square metres of wall you do not paint. Tins are rounded up, so you will usually have a little spare for touch-ups.
The link saves your inputs so you can bookmark or share this exact result.
Paint coverage by tin size
Working the other way round, here is roughly how much wall a standard tin covers at 12square metres per litre, the mid-range figure most matt emulsions print on the label. Smooth, previously painted walls are near the top of a tin's range; bare plaster, textured surfaces and strong colour changes cover less.
| Tin size | One coat | Two coats |
|---|---|---|
| 750 ml | about 9 m2 | about 5 m2 |
| 1 litre | about 12 m2 | about 6 m2 |
| 2.5 litre | about 30 m2 | about 15 m2 |
| 5 litre | about 60 m2 | about 30 m2 |
| 10 litre | about 120 m2 | about 60 m2 |
Figures are rounded and assume 12 m2 per litre. Always check the coverage printed on your specific tin, since primers, one-coat paints and exterior masonry paints differ.
How the paint quantity is worked out
The calculator measures the four walls of a room and turns that into litres of paint. Wall area is 2 times length plus width, multiplied by the wall height, which is the perimeter times the height. It then subtracts roughly 1.8 square metres for every door and window you list, so you are not buying paint for surfaces you will not roller.
Litres needed is the paintable area multiplied by the number of coats, divided by the coverage in square metres per litre printed on the tin. The litres are then divided by 2.5 and rounded up, because paint is sold in whole tins and a part tin still has to be bought.
How to use the paint calculator
- Enter the room length, width and wall height in metres.
- Set how many doors and windows are on those walls, then choose the number of coats.
- Adjust the coverage figure to match your tin, then read off the litres and the number of 2.5 litre tins to buy.
Worked examples
Standard bedroom, two coats
Inputs: 4 m by 3 m room, 2.4 m walls, two openings, two coats, coverage 11 square metres per litre
Result: Paintable area about 30 square metres, around 5.5 litres of paint, which rounds up to three 2.5 litre tins.
Single coat over the same room
Inputs: Same room but one coat instead of two
Result: About 2.7 litres needed, still two 2.5 litre tins because the first tin does not cover it on its own.
Limitations and common mistakes
Edge cases and limitations
- It sizes the four walls only. Ceilings, skirting and woodwork use different products and must be measured separately.
- Bare plaster, textured walls and big colour changes drink more paint, so lower the coverage figure if any of those apply.
- Each opening is a flat 1.8 square metres, which is a rough average for a UK door or window rather than an exact deduction.
Common mistakes
- Forgetting to multiply by the number of coats, which leaves you a tin short halfway through the second pass.
- Trusting the headline coverage on the tin for a tricky surface, when real coverage on bare or dark walls is often well below it.
Frequently asked questions
How much paint do I need for one room?
For a 4 m by 3 m room with 2.4 m walls and two openings, the paintable wall area is about 30 square metres. At two coats and 11 square metres per litre that is roughly 5.5 litres, so you would buy three 2.5 litre tins.
How many square metres does a litre of paint cover?
Most matt emulsions quote 10 to 13 square metres per litre on the tin, so 11 to 12 is a fair default. Textured walls, bare plaster and dark-over-light colour changes drink more paint, so drop the coverage figure if any of those apply.
How much does a 5 litre tin of paint cover?
At a typical 12 square metres per litre, a 5 litre tin covers about 60 square metres in one coat, or roughly 30 square metres if you are doing the usual two coats. That is enough for two coats on an average 3 to 4 metre bedroom. See the coverage table above for the other tin sizes.
How much does 2.5 litres of paint cover?
A 2.5 litre tin covers about 30 square metres in one coat at 12 square metres per litre, or around 15 square metres over two coats. A 1 litre tin covers roughly 12 square metres one coat, and 10 litres covers about 120 square metres one coat.
Should I count the ceiling?
No. This calculator sizes the four walls only. Ceilings, woodwork and trim use different products and coverage, so measure and buy those separately rather than rolling them into the wall total.
Related calculators
Tile Calculator
Find how many tiles to buy from the area and tile size, including a waste allowance.
Concrete Calculator
Estimate concrete volume and 25 kg bags for a slab, with a 10 percent waste buffer.
Mulch Calculator
Convert bed size and depth into mulch volume, litres, 50 litre bags and cubic yards.
Raised Bed Soil Calculator
Work out the soil to fill a raised bed in cubic metres, litres and 50 litre bags.
See all home & garden calculators.