UK DIY Cost Calculator
Paint Cost Calculator
Work out how much paint a room needs and what it will cost. Enter your wall measurements, the number of coats and your paint's coverage and price — you'll get litres required, tins to buy and a full cost breakdown.
Your project
Estimate
Estimates are for guidance only. Coverage rates, pack sizes and prices vary by brand — always confirm quantities with your supplier before buying.
How to work out paint for a room
Measuring paint comes down to three things: the wall area, how many coats you're applying, and the coverage rate of the paint you've chosen. This calculator takes the room's perimeter, multiplies by the wall height, subtracts a standard allowance for doors and windows, then divides by your paint's stated coverage to give litres. Because paint is sold in fixed tin sizes, it rounds up to whole tins and shows how much you'll have left over.
Coverage rates to expect
Most matt emulsions cover around 12–14 m² per litre on smooth, previously painted walls. Fresh plaster, bare masonry and strong colour changes all reduce that figure, so drop the coverage number if you're painting a challenging surface. The coverage printed on your tin is measured on ideal walls, so treating it as a best case rather than a guarantee is the safer approach.
Why two coats is the usual answer
One coat rarely gives an even finish, especially over a different colour. Two coats is standard for most rooms; three is worth budgeting for when going from a dark colour to a pale one, or when painting bare plaster where the first coat soaks in as a mist coat.
Frequently asked questions
How much paint do I need for an average room?
A typical 4m x 3m room with a 2.4m ceiling needs roughly 5–6 litres for two coats of emulsion, which is usually three 2.5-litre tins or one large tub. This calculator gives an exact figure for your own measurements.
Does this include the ceiling?
No, it calculates walls only, since ceilings are often a different paint. Add your ceiling separately by entering its length and width as a second calculation with the height set to cover the ceiling area.
Why does it subtract doors and windows?
Each door and window is wall area you won't paint, so leaving them in would make you over-buy. The calculator uses standard sizes; if your openings are unusually large, this is one reason to keep the leftover paint as a buffer.