How Much Paint Do I Need for a Room?
Measure the room's perimeter × wall height for the wall area, subtract about 21 sq ft per door and 15 per window, then divide by the paint's coverage (typically 350–400 sq ft per gallon) and multiply by the number of coats. A 12 × 12 room with 8-foot walls needs about 2 gallons for two coats.
The formula
gallons = (perimeter × height − doors × 21 − windows × 15) × coats ÷ coverage per gallon
Perimeter is the total length of all the walls: 12 + 12 + 12 + 12 = 48 feet for a 12 × 12 room. A standard door is about 3 × 7 feet (21 sq ft) and an average window about 3 × 5 feet (15 sq ft).
Worked example
A 12 × 12 bedroom, 8-foot ceilings, one door, two windows, two coats of eggshell:
- Wall area: 48 × 8 = 384 sq ft
- Openings: 21 + 2 × 15 = 51 sq ft
- To paint: 384 − 51 = 333 sq ft
- Paint: 333 × 2 coats ÷ 380 sq ft per gallon = 1.75 gallons, so buy 2 gallons
Paint by room size
| Room | Walls | Wall area to paint | 1 coat | 2 coats |
|---|---|---|---|---|
| 10 × 10 | 8 ft, 1 door, 1 window | 284 sq ft | 1 | 2 |
| 10 × 12 | 8 ft, 1 door, 1 window | 316 sq ft | 1 | 2 |
| 12 × 12 | 8 ft, 1 door, 2 windows | 333 sq ft | 1 | 2 |
| 12 × 14 | 8 ft, 1 door, 2 windows | 365 sq ft | 1 | 2 |
| 14 × 16 | 8 ft, 1 door, 2 windows | 429 sq ft | 2 | 3 |
| 15 × 20 | 8 ft, 1 door, 3 windows | 494 sq ft | 2 | 3 |
| 14 × 16 | 9 ft, 1 door, 2 windows | 489 sq ft | 2 | 3 |
Rounded up to whole gallons. When the exact amount is just over a gallon line, a gallon plus a quart or two is often cheaper than another full gallon.
Step by step
- Measure each wall's length and add them up for the perimeter.
- Measure the wall height, floor to ceiling.
- Count doors and windows. Large openings like patio doors or picture windows: measure them instead.
- Find your paint's coverage on the can or its data sheet. Glossier finishes usually spread a little less.
- Do the math and round up to what the store sells.
Common mistakes
- Using floor area. A 12 × 12 room is 144 sq ft of floor but 384 sq ft of wall.
- Forgetting the second coat. Most repaints that change color need two.
- Assuming the top of the coverage range. Textured walls, fresh drywall and big color changes all use more.
- Leaving out primer on new drywall, patched walls or dark-to-light changes.
Estimates use typical coverage by finish (flat 400, eggshell 380, satin 375, semi-gloss 350, high gloss 325 sq ft per gallon). Your paint's label is the number to buy by.
Questions
How much paint for a 12 × 12 room?
About 2 gallons for two coats on the walls, with 8-foot ceilings, one door and two windows. That's 333 square feet of wall at about 380 square feet per gallon.
How much paint for a 10 × 10 room?
About 1.5 gallons for two coats with 8-foot walls, one door and one window, so buy 2 gallons, or 1 gallon plus 2 quarts if you'd rather not have leftovers.
Does the ceiling need separate paint?
Usually. Ceiling area is length × width (144 sq ft for a 12 × 12 room), and most people use a flat ceiling paint rather than the wall color.
Do I need two coats?
Usually yes for a color change or a new finish, and always on fresh drywall after primer. One coat can be enough when repainting the same color in good condition.