How much paint for a room? The calculator
Enter the room’s measurements, its doors, windows and the number of coats: the calculator gives the cans of paint to buy.
People often buy too much paint, or not enough to finish the last wall. The right amount comes down to three things: the wall area, the openings and the number of coats.
The calculator
Enter your measurements, in feet or metres. The result changes with every number.
Walls
2 cans of 3.78 L
302 sq ft to paint, 2 coats, about 6.5 L.
The calculation, step by step
Take a 12 × 10 ft bedroom with 8 ft walls, one door and two windows.
- The wall area: the room's perimeter times its height. 2 × (12 + 10) × 8 = 352 sq ft.
- Less the openings: 20 sq ft (1.9 m²) per door and 15 sq ft (1.4 m²) per window. 352 − 20 − 30 = 302 sq ft.
- Times the number of coats: with two coats, 604 sq ft.
- Divided by the coverage: a 3.78 L can covers about 350 sq ft (32.5 m²) in one coat on a smooth wall. 604 ÷ 350 = 1.7, so 2 cans of 3.78 L.
Makers state 350 to 400 sq ft per 3.78 L can. The calculator takes the low end of the range: a textured wall or a dark colour takes more.
How many coats?
- Two coats in most cases. That is what gives an even colour, without roller marks.
- One coat is sometimes enough to refresh the same colour.
- A primer first on new drywall, or to go from a dark colour to a light one. It is a separate product: for its amount, set the calculator to 1 coat.
Sizes in store
Paint is mostly sold in 3.78 L and 946 mL cans. The calculator combines the two, and switches to a 3.78 L can as soon as three 946 mL cans would be needed: the large size then usually costs less.
Three tips
- Have all the paint tinted at once. Two tintings can give two slightly different shades.
- Keep a little paint for touch-ups.
- The ceiling is done separately, with ceiling paint. Tick it in the calculator to get its amount.