Paint Calculator
How many gallons or quarts of paint a room takes, from your dimensions and number of coats, with doors and windows already subtracted from the wall area.
Gallons to buy
3gal
Exact gallons
2.38gal
Or in quarts
10qt
Wall area
417ft²
Based on 350 sq ft per gallon, the usual rate for interior latex on primed drywall. Textured or unprimed walls drink more than that, so buy an extra gallon if either applies.
How the paint calculator works
Wall area is the perimeter of the room times its height, minus a standard allowance for doors and windows. That net area gets multiplied by your number of coats, then divided by a can's typical coverage rate.
Formula: wall area = 2 × (length + width) × height − (doors × 21) − (windows × 15). Gallons = (wall area × coats) ÷ 350.
We round up to the next whole gallon, or quart for small rooms, because that's how paint is sold. Round up in your own head too if the walls are textured or unprimed: 350 sq ft per gallon assumes a smooth primed surface, and texture can eat 20 to 30% of that.
Want the reasoning behind the number? We cover how much a gallon of paint actually covers, how much paint you need room by room, and whether a 5-gallon bucket is worth buying.
Frequently asked questions
Most rooms take 2 to 3 gallons for two coats. A 12x12 ft room with 8 ft ceilings needs about 2; a 12x14 ft room with 9 ft ceilings needs 3. The figure comes from wall area, not floor area, so two rooms with the same square footage can need different amounts of paint. Enter your dimensions above for your own number.
No, walls only. Ceiling area is just the room's length times width, and it usually takes a different product anyway, a flat ceiling paint, not the wall finish. Budget about a gallon per 350 sq ft of floor area per coat on top of what this calculator gives you.
Two, for a color change or new drywall. One is enough for touch-ups or repainting the same color, and you can set coats to 1 above to see that. Going from white to a deep navy, red, or yellow often takes three no matter what the can promises, because those pigments are less opaque.
Because you aren't painting them, at least not with wall paint. Taking out 21 sq ft per door and 15 sq ft per window keeps the estimate from sending you home with a gallon you didn't need. Those are averages, so a room with a patio slider or a picture window will come out a little high.
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