Paint Calculator
Enter your room dimensions and number of coats to find out how many gallons or quarts of paint you'll need, minus doors and windows.
Gallons to buy
3gal
Exact gallons
2.38gal
Or in quarts
10qt
Wall area
417ft²
Coverage assumes 350 sq ft per gallon, the typical rate for interior latex paint on primed drywall. Textured or unprimed surfaces may need more.
How the paint calculator works
Wall area is calculated as the perimeter of the room times its height, minus a standard allowance for doors and windows. That net area is then multiplied by your number of coats and divided by a can's typical coverage rate.
Formula: wall area = 2 × (length + width) × height − (doors × 21) − (windows × 15). Gallons = (wall area × coats) ÷ 350.
The result is rounded up to the nearest whole gallon (or quart, for small rooms) since paint is sold in fixed container sizes.
Frequently asked questions
About 350 square feet per coat on primed drywall, which is the industry-standard figure most paint manufacturers print on the can. Textured, unprimed, or dark-to-light color changes can lower coverage significantly.
This calculator estimates wall paint only. Ceilings are calculated separately as length × width of the room, usually with ceiling-specific flat paint.
Two coats is standard for a color change or new drywall. A single coat can work for touch-ups or repainting the exact same color, which you can reflect by setting coats to 1.
Doors and windows aren't painted the same as walls, so subtracting their average area (21 sq ft per door, 15 sq ft per window) keeps the estimate from overestimating how much paint you need.