Enter your room dimensions and this tool works out wall area, then how much paint to buy — accounting for doors, windows, number of coats, and whether you need primer. Imperial and metric.
This tool gives estimates for planning purposes only and isn’t a substitute for professional measurement, a site inspection, or your local building code and supplier guidance. Always verify quantities and code requirements before purchasing materials or beginning work.
Wall area is the room's perimeter times ceiling height, minus a standard allowance for doors and windows: 2(length + width) × height, minus 21 sq ft per door and 15 sq ft per window. Multiply by the number of coats to get total painted area, then divide by your paint's coverage rate to get gallons.
Worked example: a 12 × 10 ft room, 8 ft ceilings, 1 door, 2 windows, 2 coats, 350 sq ft/gal coverage: wall area = 2(12+10)×8 − 21 − 30 = 301 sq ft. Two coats = 602 sq ft ÷ 350 = 1.75 gallons — round up to 2 gallons.
Primer is its own coat with its own coverage rate, typically similar to topcoat (300–400 sq ft/gal). This tool adds one primer coat's worth of area when you select "needs primer," on top of your regular topcoats.
Wall area (perimeter × height, minus doors and windows) divided by your paint's coverage rate — usually 350–400 sq ft per gallon (about 32–37 m² per 4L can) — gives you the amount needed per coat. Multiply by your number of coats.
Two coats is standard for a color change or new drywall. One coat can work when repainting the same color on a surface already in good condition. Dark-to-light color changes or stain-blocking situations may need a primer coat plus two topcoats.
Yes for: new drywall or bare wood, major color changes (especially dark to light), water stains, or repairs. Primer isn't needed when repainting a similar color over a sound existing coat — self-priming "paint and primer in one" products still perform best with proper prep, not as a full substitute on bare surfaces.
Most quality wall paints cover 350–400 sq ft per gallon in one coat on primed drywall. Textured surfaces, unprimed drywall, or very absorbent surfaces reduce coverage — check your specific product's label, since coverage varies by brand and finish.
Yes — always round up to the next full can size, and buy from the same batch/lot number where possible to avoid slight color variation between cans on the same wall.