The Wall Paint Calculator works out how much paint you need for a single wall — such as an accent wall — or several walls together. Enter the total wall length and height, the doors and windows to subtract, the number of coats and the coverage from the can.
Wall Paint Calculator
Paint for one wall or several walls, minus doors and windows, in gallons and litres.
Results are given in gallons and liters, along with how many gallon cans to buy.
Formula
Paintable area = L × H − 21 ft² × doors − 15 ft² × windows
Paint = paintable area × coats ÷ coverage
Where L = total length of the walls being painted and H = wall height.
How the Calculation Works
Step 1: Add the lengths of all walls you are painting.
Step 2: Multiply by height and subtract openings.
Step 3: Multiply by coats and divide by coverage.
Example Calculation
Given: one 12 ft wall, 8 ft high, 1 window, 2 coats, 350 ft²/gal
Paintable = 96 − 15 = 81 ft²
Paint = 81 × 2 ÷ 350 ≈ 0.46 gal (≈ 1.75 L)
That is just under half a gallon; a gallon can is the round-up, or two quarts would cover it.
Units and Dimensions
| Container | US volume | Liters |
|---|---|---|
| Quart | 0.25 gal | 0.95 L |
| Gallon | 1 gal | 3.79 L |
| 5-gallon pail | 5 gal | 18.9 L |
Material Estimation Notes
- Coverage varies with the surface; textured or porous walls use more paint.
- Dark or saturated colors may need an extra coat or tinted primer.
- For a whole room including ceiling, use the Paint Calculator.
Frequently Asked Questions
How much paint do I need for one wall?
Wall area minus openings, × coats ÷ coverage. A 12 × 8 ft wall with one window needs about 0.46 gal for two coats.
How do I calculate the square footage of a wall?
Length × height.
Is a quart enough for an accent wall?
A quart covers roughly a quarter of a gallon’s coverage — often too little for two coats on a full wall.
Should I subtract windows?
Yes, openings aren’t painted.
What about several walls of different heights?
Calculate each separately and add the paint amounts.