Paint Calculator
Work out how much paint you need for walls and ceilings, and which cans to buy.
How to use the Paint Calculator
- 1Enter the room's length, width and wall height, or measure wall by wall.
- 2Add doors and windows, choose the number of coats and the coverage printed on the can.
- 3Enter the can sizes and prices from your store to get the cheapest mix of cans.
About Paint Calculator
The Paint Calculator works out how much paint a room needs. Enter the length, width and wall height of the whole room, or switch to wall-by-wall measuring when the walls differ in size, then add doors, windows and other openings so they are taken off the wall area. You can include the ceiling, choose one to three coats, enter the coverage printed on the can and pick the surface: textured finishes such as woodchip add 10%, rough or porous surfaces such as brick or fresh plaster add 25%. A waste allowance covers rollers, trays and touch-ups.
Beyond the total in litres or gallons, the calculator turns the result into cans. Enter the can sizes and prices from your store and it finds the cheapest mix of cans, or the mix with the least paint left over if you skip the prices. A table compares buying only one can size, and an optional primer coat gets its own coverage and can count. Metric (m², litres) and imperial units (sq ft, US gallons and quarts) are both supported, and every step of the calculation is shown.
Use this paint calculator before a weekend repaint, when freshening up a rented apartment or when quoting a small painting job, so you buy enough paint from one batch without a pile of unopened cans afterwards.
Frequently asked questions
How much paint do I need per square meter?
Most wall paints cover 8 to 12 m² per litre and coat, or about 350 to 400 sq ft per gallon. Two coats double the amount, and textured or porous surfaces take more.
Do I need two coats of paint?
Usually yes. A second coat evens out the color and covers roller marks. One coat can be enough when repainting in a similar color with a high-quality paint.
Should I subtract doors and windows?
Yes for full-size doors and windows. Small openings such as sockets and switches are not worth subtracting; the waste allowance covers them.
How do I calculate the wall area of a room?
Add up the lengths of all walls (the perimeter) and multiply by the wall height. A 4 × 3 m room with 2.5 m high walls has 14 m × 2.5 m = 35 m² of wall before doors and windows are subtracted.
When do I need a primer before painting?
Primer is worth it on new drywall, fresh plaster, bare wood, stained areas and when covering a dark color with a much lighter one. It seals the surface so the topcoat absorbs evenly, which can save an extra coat of the more expensive paint.
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