Paint Calculator — How Much Paint for a Room or Wall

Buying paint is a two-guess problem: guess too little and you are back at the store mid-wall, guess too much and the surplus dries out on a shelf. This calculator replaces the guessing with the same arithmetic a decorator uses — surface area, minus openings, times coats, divided by the paint's coverage — and then translates the result into actual cans to buy.

In room mode you enter length, width and ceiling height, and the wall area is computed as perimeter × height; in area mode you type the square meters directly, which suits a single wall, a ceiling (length × width) or a facade. Doors and windows are subtracted at standard sizes — 1.9 m² per door, 1.4 m² per window — and both the number of coats and the coverage are editable, with 11 m² per liter as a realistic default for wall paint on smooth plaster.

The answer comes in three forms: the net area you will actually paint, the liters required, and a suggested combination of standard can sizes (1, 2.5, 5 and 10 L) that covers the job with minimal leftover. A separate line restates the job in imperial terms — square feet and US gallons at the common 350 sq ft per gallon rule — for paint sold in gallon cans.

Coverage is the honest variable: it is printed on every can as a range, and rough, porous or unprimed surfaces land at the low end. Check your paint's own figure, prime fresh plaster, and plan around 10% reserve for touch-ups. Like every tool on this site, the calculator runs entirely in your browser — nothing you enter is uploaded or stored.