Paint calculator
How many gallons of paint a room needs, after taking out doors and windows, for any number of coats.
- Wall area to paint
- Ceiling
Doors are counted as 21 sq ft (3 × 7 ft) and windows as 15 sq ft (3 × 5 ft). Check your paint can for its exact coverage.
How to use it
Enter the room's length, width and wall height in feet, plus how many doors and windows it has. Two coats is the usual choice, especially when changing color. The calculator works out the wall area to paint and how much paint to buy, rounded up to whole gallons and quarts.
Set the coverage to the figure on your paint can if you have it. Tick Paint the ceiling too to see the ceiling separately, since ceiling paint is usually a different product.
How it's calculated
- Wall area = 2 × (length + width) × height.
- Subtract 21 sq ft per door and 15 sq ft per window.
- Gallons = area × coats ÷ coverage per gallon.
- Round up to the nearest quart. Three quarts are rounded up to a gallon, which usually costs about the same.
How far does a gallon go?
Most interior wall paint covers 250 to 400 square feet per gallon per coat. The calculator starts at 350, a middle value. Coverage drops when:
- the surface is rough, textured or porous, like new drywall or bare wood
- you use a higher-sheen paint, which tends to go on thinner
- you roll on a darker color over a light one, or a light color over a dark one, which can need an extra coat
| Room | Wall area (1 door, 2 windows) | 2 coats at 350 sq ft/gal | Buy |
|---|---|---|---|
| 10 × 10 ft, 8 ft walls | 269 sq ft | 1.54 gallons | 2 gallons |
| 12 × 12 ft, 8 ft walls | 333 sq ft | 1.90 gallons | 2 gallons |
| 12 × 15 ft, 9 ft walls | 435 sq ft | 2.49 gallons | 2 gallons + 2 quarts |
Tips
- Prime new drywall and stained or glossy surfaces. Primer usually covers less per gallon than paint, so check its label.
- Buy all the paint for a room at once, from the same batch if you can. Tints can vary slightly between batches.
- Keep a little left over for touch-ups. Label it with the room and the date.