How much paint do I need for a room?

Enter each wall width and height, then subtract doors and windows. The calculator divides total square footage by paint coverage per gallon (typically 350 to 400 square feet) and shows gallons needed for one or two coats.

How do I calculate paint coverage for multiple coats?

The calculator doubles the square footage for two coats before dividing by coverage per gallon. If your walls total 800 square feet, two coats mean 1,600 square feet of coverage needed, and the calculator shows exactly how many gallons that requires.

Should I subtract doors and windows from paint estimates?

Yes, subtracting trim elements keeps you from overbuying. The calculator automatically deducts standard door area (roughly 21 square feet) and window area (roughly 15 square feet) from your wall total to give a more accurate gallon count.

Finishes

Paint Coverage Calculator

Subtract doors and windows automatically, compare one or two coats, and estimate total gallons required.

Use this free Paint Calculator to turn room measurements into a practical paint estimate before you buy. Add your wall dimensions, openings, coats, and coverage rate, and it does the gallon math for you. It’s built for quick DIY planning and contractor takeoffs, without the guesswork at the paint counter.

How it works

Start with wall area: perimeter in feet x wall height in feet = total wall square footage. Then subtract areas you won’t paint. A standard door is about 21 sq ft, and a standard window is about 15 sq ft. Formula: paintable area = wall area - door area - window area. Next, multiply by the number of coats: total paint area = paintable area x coats. One gallon typically covers about 350 to 400 sq ft per coat, so divide your total paint area by your selected coverage rate. Final formula: gallons needed = total paint area / coverage per gallon. Always round up, because paint is sold by the can and touch-ups matter.

Worked examples

Interior bedroom Perimeter 48 ft, wall height 8 ft, 1 door, 2 windows, 2 coats, coverage 350 sq ft per gallon Wall area: 48 x 8 = 384 sq ft. Subtract openings: 1 door x 21 = 21 sq ft, 2 windows x 15 = 30 sq ft. Paintable area: 384 - 51 = 333 sq ft. Total coat area: 333 x 2 = 666 sq ft. Gallons: 666 / 350 = 1.9. Round up to 2 gallons.
Small bathroom Perimeter 28 ft, wall height 8 ft, 1 door, 1 window, 2 coats, coverage 400 sq ft per gallon Wall area: 28 x 8 = 224 sq ft. Subtract openings: 1 door x 21 = 21 sq ft, 1 window x 15 = 15 sq ft. Paintable area: 224 - 36 = 188 sq ft. Total coat area: 188 x 2 = 376 sq ft. Gallons: 376 / 400 = 0.94. Round up to 1 gallon.
Exterior paint estimate Perimeter 120 ft, wall height 10 ft, 2 doors, 6 windows, 2 coats, coverage 350 sq ft per gallon Wall area: 120 x 10 = 1200 sq ft. Subtract openings: 2 doors x 21 = 42 sq ft, 6 windows x 15 = 90 sq ft. Paintable area: 1200 - 132 = 1068 sq ft. Total coat area: 1068 x 2 = 2136 sq ft. Gallons: 2136 / 350 = 6.1. Round up to 7 gallons.

FAQ

How do I calculate paint for a room?

Measure the room perimeter in feet, multiply it by wall height in feet, subtract doors and windows, multiply by the number of coats, then divide by the coverage per gallon. Round up to the next full gallon.

Should I subtract doors and windows?

Yes. A common estimating shortcut is to subtract about 21 sq ft for each door and about 15 sq ft for each window. That keeps the estimate closer to the actual paintable wall area.

How much does one gallon of paint cover?

One gallon typically covers about 350 to 400 sq ft per coat. Use the coverage listed on your paint can if you already know the product, since the calculator works best with the exact rate you plan to buy.

Why does the calculator round up?

Paint is usually bought by the gallon, and running short is frustrating. Rounding up gives you enough for full coverage, small mistakes, and later touch-ups from the same batch.