Home & DIY · 1 min read
How much paint do I need for a room?
Measure the walls, subtract the openings, multiply by coats and divide by the coverage on the can.
Last updated November 3, 2026
Step 1: wall area
Add the lengths of all walls to get the perimeter, then multiply by the ceiling height.
Worked example
A 12 ft by 14 ft room with an 8 ft ceiling
| Step | Calculation | Value |
|---|---|---|
| Perimeter | 12 + 14 + 12 + 14 | 52 ft |
| Wall area | 52 × 8 | 416 sq ft |
Step 2: subtract openings
A standard door is about 21 square feet (3 × 7 ft) and a typical window about 15. Taking away one of each leaves 416 − 36 = 380 square feet to paint.
Step 3: coats and coverage
Two coats is the usual advice, and more over a dark color. Coverage is printed on the can; around 350 square feet per gallon is a common figure, but textured walls absorb more.
Formula
gallons = area × coats ÷ coverage
- area
- square feet to paint
- coats
- number of coats
- coverage
- square feet per gallon, from the can
Worked example
380 sq ft, two coats, 350 sq ft per gallon
Result: 380 × 2 ÷ 350 ≈ 2.2, so buy 3 gallons
If the shop sells quarts, 2 gallons plus a quart also covers it.
Tips
Tip
- Round up: running short means a second batch that may not match exactly.
- Primer is separate from paint and has its own coverage.
- Ceilings and trim are measured and bought separately.