What it works out
Work out how much paint a room needs. Enter the length, width and height, say whether the ceiling is painted, and take off the doors and windows. You get the area to paint, the paint for every coat and an order rounded up to whole containers. Waste starts at the usual figure for the trade; change it in the tool. Coverage depends on the paint and the surface, so use the figure on the can when it differs.
The formula
- Area
- 2 × height × (length + width) (+ length × width with the ceiling) − openings
- Paint
- area × coats ÷ coverage
In words: Area = 2 times height times (length plus width), plus length times width with the ceiling, minus openings; paint = area times coats divided by coverage
Worked example
A 12 ft by 10 ft room with 8 ft walls, ceiling not painted, 36 ft² of doors and windows, two coats at 350 ft² per gallon
- Length 12 ft
- Width 10 ft
- Height 8 ft
- Openings 36 ft²
- Coats 2
- Coverage 350 ft² per gallon
- Walls = 2 × 8 × (12 + 10) = 352 ft²
- Area to paint = 352 − 36 = 316 ft²
- Paint = 316 × 2 ÷ 350 = 1.81 gal
The order rounds up to whole containers after waste.
Good to know
- Coverage depends on the paint and surface: use the figure on your can.
- Trim, closets and second ceilings are separate areas.
- A calculator, not a building-code check: confirm local rules with your building authority.
Questions
What coverage should I use?
The figure printed on the can for your surface. Rough or dark surfaces need more.
Is the ceiling included?
Only if you choose to paint it.