Paint Calculator
Estimate how much paint a room needs from its wall area, the number of coats, and deductions for doors and windows. Get the answer in litres and see how many standard tins to buy.
How to use this calculator
- Add up the wall lengths (or use 2 × (length + width)) and enter the height.
- Set the number of coats — 2 is standard, more when changing colour drastically.
- Deduct doors and windows, and check the coverage figure on your paint tin.
Formula used
Standard deductions used here: ~1.8 m² per door, ~1.5 m² per window. Coverage is typically 10–13 m² per litre for emulsion, but varies by paint and surface — the tin's stated figure wins.
Example calculation
A room with 20 m perimeter × 2.5 m high = 50 m² gross. Minus 1 door (1.8) and 2 windows (3.0) = 45.2 m² paintable.
Two coats = 90.4 m² ÷ 11 m²/L = 8.2 litres — so two 5 L tins.
Why paint estimates run short
The commonest painting mistake is buying for one coat when you need two — most colours, and nearly all colour changes, require two coats for even coverage, doubling the paint. Bare plaster, patched areas and dark-to-light changes often add a primer coat on top of that.
The coverage figure is where estimates drift: manufacturers quote an ideal m²-per-litre on smooth, sealed surfaces, but textured, porous or thirsty walls drink more. When in doubt, round up and keep the leftover — touch-ups from the same batch match perfectly, while a fresh tin bought later can differ subtly in shade.
Why use this calculator?
- Account for coats and openings, the two things guesswork gets wrong.
- Convert litres straight into tins to buy.
- Adjust coverage to your actual paint and wall type.
Frequently asked questions
How much paint do I need for one room?
For an average room (around 45–50 m² of wall) at two coats, roughly 8–10 litres. Enter your exact perimeter, height, coats and openings above for a precise figure.
How many coats of paint do I need?
Two is standard for good coverage. One coat can work when repainting the same colour on a sealed surface; drastic colour changes or bare surfaces may need a primer plus two topcoats.
Does the ceiling count?
This calculator covers walls only. For the ceiling, calculate its area separately (length × width of the room) and divide by the coverage figure — ceilings usually take one to two coats.