Home and everyday
Paint Calculator for a Room
How many gallons of paint you need for your room
With this paint calculator you type the length, width and height of the room, and we tell you the square feet of wall and the gallons of paint you need.
The key idea
Paint is not measured by the floor: it is measured by the walls
A 12 × 10 ft room has 120 sq ft of floor, but 317 sq ft of wall with 8 ft ceilings, one door and one window. Two coats at 350 sq ft per gallon come to 1.8 gallons. With a 10% margin, buy 2 gallons.
How it is calculated
Walls = 2 × (length + width) × height − openings
Gallons = sq ft × coats / coverage per gallon
We subtract 20 sq ft per door (a 3 × 6⅔ ft door) and 15 sq ft per window (3 × 5 ft); if yours are much bigger or smaller, adjust the count. Coverage per gallon is printed on the label of the can, so check it and type your number. Porous walls, new drywall or a big color change use more paint.
Worked example
A 12 × 10 ft room with 8 ft ceilings, one door and one window: 2 × 22 × 8 − 20 − 15 = 317 sq ft. Two coats at 350 sq ft per gallon: 1.8 gallons. With a 10% margin, buy 2 gallons.
Typical cases
How much paint for a room by size
Paint for the walls of common room sizes with 8-foot ceilings, one door, one window, two coats and 350 sq ft per gallon.
| Room size (ft) | Wall area | Paint needed | Buy |
|---|---|---|---|
| 8 × 10 | 253 sq ft | 1.4 gal | 2 gal |
| 10 × 10 | 285 sq ft | 1.6 gal | 2 gal |
| 10 × 12 | 317 sq ft | 1.8 gal | 2 gal |
| 12 × 12 | 349 sq ft | 2.0 gal | 3 gal |
| 12 × 14 | 381 sq ft | 2.2 gal | 3 gal |
| 12 × 16 | 413 sq ft | 2.4 gal | 3 gal |
| 14 × 16 | 445 sq ft | 2.5 gal | 3 gal |
| 15 × 20 | 525 sq ft | 3.0 gal | 4 gal |
| 16 × 20 | 541 sq ft | 3.1 gal | 4 gal |
| 20 × 20 | 605 sq ft | 3.5 gal | 4 gal |
Save or share this table as an image Common questions
Frequently asked questions
How much paint do I need per square foot?
At 350 sq ft per gallon, you need about 0.0029 gallons per square foot per coat, or 1 gallon for every 175 sq ft with two coats. The exact coverage is on the label and depends on the paint and the wall.
Do I need a second coat?
Almost always, especially if you are changing color. The first coat covers and the second evens out the finish.
How much extra paint should I buy?
About 10% more than the estimate: it covers touch-ups and keeps you from running out halfway through a wall. The calculator already rounds that figure up to whole gallons and also shows it in quarts.
How much do you subtract for doors and windows?
We subtract 20 sq ft per door and 15 sq ft per window. If you have a sliding glass door or a large picture window, the real opening is bigger and you will need a little less paint.
Is the ceiling included?
Only if you check “Paint the ceiling too”: then we add length times width. If you use a different paint on the ceiling, run it separately with that paint's coverage.
Why did I use more paint than calculated?
Because porous walls, new drywall and strong color changes soak up more than the label says. In those cases, use a primer first or plan one more coat.
Home and trips
Home and everyday
You may also need
Your next calculation
Missing a calculator?
Tell us what you need to calculate. The most requested ones are the first we build, with their formula, a worked example and the source.