Free paint calculator. Find out how many liters and cans of paint you need for a room, based on wall dimensions, number of coats, and door/window openings.
To calculate paint needed: multiply wall length by height to get wall area, subtract the area of doors and windows, then multiply by the number of coats. Divide the result by your paint's coverage rate (m2 per liter) to get the liters needed, adding 5-10% extra for waste.
10.12 L
Paint needed
5
Cans needed
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Paint Calculator
Estimating paint accurately avoids two costly mistakes: buying too little (requiring a second trip and risking a slightly different batch color) or buying too much (wasted money on unused paint). The calculation starts with wall area, then adjusts for openings, coats, and coverage rate.
The Formula
Wall area = total wall length x wall height. From this, subtract the combined area of doors and windows to get the actual paintable area. Multiply by the number of coats (usually 2), since each coat needs its own paint volume — painting two coats over 40 m² requires paint for 80 m² of coverage, not 40.
Coverage Rate
A paint can's stated coverage rate (e.g., 10 m²/L) assumes a smooth, primed, non-porous surface applied at the recommended thickness. Rough, textured, or unprimed surfaces absorb more paint and reduce actual coverage — sometimes by 20-30%. When in doubt, use the lower end of the manufacturer's stated coverage range.
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For related home improvement calculations, see our tile calculator, concrete calculator, and landscape calculator.
Practical Use Cases
Room renovation
Estimating exact paint quantity before a DIY room repaint to avoid over- or under-buying.
Getting contractor quotes
Cross-checking a painter's quoted material quantity against your own estimate.
Budgeting a project
Calculating total paint cost before starting a home improvement project.
Multi-room projects
Adding up paint needs across several rooms to buy in bulk and save on cost per liter.
Exterior painting
Estimating paint needed for larger exterior wall surfaces, accounting for texture-related coverage loss.
Multiply the total wall length by the wall height to get the wall area, subtract the area of doors and windows, multiply by the number of coats, then divide by your paint's coverage rate (found on the can label, usually in m2/L or ft2/gallon).
Two coats is standard for most walls, especially when changing color or painting over a darker shade. A single coat may suffice for touch-ups or repainting the same color; three coats are sometimes needed for very light colors over dark surfaces or for high-visibility accent walls.
Subtract the full opening (frame included) for windows and doors — you won't be painting over them. For small windows, some painters skip the deduction since the waste allowance already covers minor overestimates, but for large windows or multiple doors, subtracting accurately matters.
Paint is lost to roller absorption, tray residue, drips, and touch-ups. A 5-10% waste allowance on top of the calculated area ensures you don't run short mid-project and need to color-match a second batch.
It's printed on the paint can label, usually as "coverage" or "spreading rate," typically 8-12 m2 per liter (350-400 sq ft per gallon) for a single coat on a primed, smooth surface. Textured or porous surfaces reduce coverage.