Paint calculator
How much paint do you need? Enter your room, pick coats and get gallons and quarts to buy, with a cost range. No sign-up.
Each door counts as 21 sq ft and each window as 15 sq ft. Two coats is the usual advice for a color change; check the coverage printed on your can.
Paint to buy
2 gallons
1.72 gallons needed
Paint cost
$50-$100
At $25-$50 per gallon
Wall area
301 sq ft
After doors and windows
Total to cover
602 sq ft
2 coats
Not sure on the color yet?
Try 150 real paints in the paint color visualizer or build a room scheme with the palette generator.
Preview a color on your room first
Before you buy gallons, see a color on your own walls. The calculator is free; the AI preview on your photo needs a free account.
Your photo stays in this browser until you sign up. Free account required for AI renders; eligible new accounts get free credits, and free results carry a small watermark.
Estimates, sources
Coverage, door and window sizes and prices are published rules of thumb, not measurements of your room. Your can's label is the final word on coverage.
- How Much Paint Do I Need? (Bob Vila, 2022): manufacturers estimate 250-400 sq ft per gallon; a quart covers about 100 sq ft
- Paint Calculator (Housecall Pro, 2025): doors about 21 sq ft, windows about 15 sq ft each
- How Much Does It Cost to Hire a Painter? (HomeAdvisor, 2026): a gallon averages $25-$50, designer paints over $100; pro interior painting $2-$6 per sq ft
The formula
Wall area is the room's perimeter times its height: 2 x (length + width) x height. Subtract about 21 sq ft per door and 15 sq ft per window. Multiply by the number of coats, then divide by the coverage on the can. Manufacturers quote roughly 250 to 400 sq ft per gallon; 350 is a sensible middle. A 12 x 10 ft room with 8 ft walls, one door and two windows has about 301 sq ft of wall, so two coats need about 1.7 gallons: buy 2.
When to buy quarts instead of another gallon
A quart is a quarter gallon (about 100 sq ft). If you're only one or two quarts over a whole gallon, quarts are cheaper. At three quarts, a gallon usually costs about the same, so the calculator rounds up.
Pick the color before you buy
Paint is the cheapest part of the job and the most annoying to redo. Test colors in the paint color visualizer and read how to test paint colors before buying.
How it works
Measure each room
Length, width and wall height. Add rooms if you're painting more than one.
Count doors and windows
Each door takes about 21 sq ft off the wall area, each window about 15 sq ft.
Pick coats and extras
Two coats for a color change, plus the ceiling or a primer coat if you need them.
Buy the plan
Whole gallons plus quarts for small remainders, so you don't overbuy.
Questions
How much paint do I need for a 12x12 room?
With 8 ft walls, one door and two windows, a 12 x 12 room has about 333 sq ft of wall. Two coats at 350 sq ft per gallon is about 1.9 gallons, so buy 2 gallons. Add about half a gallon per coat if you also paint the ceiling.
How many coats of paint do I need?
Two coats is the standard advice for an even finish, especially when changing color. One coat can work for a refresh in the same color; very dark or very bright changes may need a primer or a third coat.
How much does a gallon of paint cover?
Manufacturers publish roughly 250 to 400 sq ft per gallon per coat depending on the product and surface. Rough or porous walls take more. Check the label on your can and adjust the coverage field.
How much does paint cost for a room?
A gallon commonly costs $25 to $50 (designer brands can top $100), so most single rooms need $50 to $150 of paint. Hiring a painter typically runs $2 to $6 per sq ft including labor. These are national estimates, not quotes.