Calculator
Paint Calculator
Estimate how many gallons of paint you need for a room.
How much paint do I need?
Paint is sold by coverage per gallon, so the real question is how many square feet you’re actually covering — wall area minus doors and windows, multiplied by how many coats you’re applying. This calculator works through that math so you buy close to the right amount instead of guessing.
Frequently asked questions
How much does one gallon of paint cover?
This calculator assumes the standard estimate of 350 square feet per gallon (about 8.6 m² per liter) for one coat on primed drywall. Textured surfaces, unprimed drywall, or very dark color changes can cut real coverage meaningfully below that, so treat it as a starting point, not a guarantee.
Why subtract doors and windows?
They're not painted the same way (or at all, with the same wall color), so counting their area as paintable wall overestimates how much you need. The calculator uses standard averages — 21 sq ft (2 m²) per door, 15 sq ft (1.4 m²) per window — which is close enough for planning purposes even though exact sizes vary.
Do I really need two coats?
For a color change, yes almost always — one coat rarely gives even coverage or true color depth, especially over a different existing color. Repainting the same color on a wall in good condition can sometimes get away with one coat, but two is the safer default this calculator assumes.
Should I round up the gallons?
This calculator already rounds up to the nearest quart. It's still worth buying a little extra beyond that for touch-ups later, since matching a color exactly months later (different batch, some fading) is harder than keeping leftover paint from the original can.
Assumes standard coverage of 350 sq ft per gallon, a 21 sq ft door and 15 sq ft window. Adjust for textured walls or different paint.