CalcCoverageHow much paint do I need?
Paint coverage is about wall area, not floor area. Add up the four walls (perimeter × height), take out the doors and windows you are not painting, multiply by the number of coats, and divide by the coverage on the can — about 350 sq ft per gallon per coat for standard interior paint.
Paint needed = (wall area − doors − windows) × coats ÷ 350 sq ft per gallon
Example: a 12 × 12 ft room with 8 ft walls has 384 sq ft of wall. Minus one door (21) and two windows (24) leaves 339 sq ft. Two coats = 678 sq ft of painting ÷ 350 = 1.94 gallons — bought as 1 gallon + 4 quarts.
Why the answer comes in gallons + quarts
Paint is sold in gallons and quarts, not decimals. Buying 1.94 gallons means one gallon can plus four quart cans (or simply two gallons if the price per quart is silly — compare at the shelf). This calculator gives you the exact total and a sensible can combination, plus liters for metric stores, where a liter covers about 10 sq m per coat.
| Surface | Allowance used here |
|---|---|
| Standard door | 21 sq ft (2.0 sq m) |
| Standard window | 12 sq ft (1.1 sq m) |
| Smooth previously-painted wall | ~350–400 sq ft / gal |
| New drywall or strong colour change | Primer + 2 coats — count the primer as a coat |