Paint Calculator
Enter your room size, doors, windows and number of coats. You get the paintable area, the paint you need in gallons and liters, the cans to buy and an optional cost estimate.
How to use the Paint Calculator
- Choose units: feet and gallons, or meters and liters.
- Enter the room length, width and wall height, or switch to Walls only and list each wall.
- Set doors and windows so their area is taken off, and tick the ceiling if you paint it.
- Pick the number of coats and check the coverage on your paint can.
- Press Estimate to see the paint needed, the cans to buy and the cost.
How to calculate how much paint you need
The formula has four steps:
- Wall area = perimeter × wall height = 2 × (length + width) × height.
- Paintable area = wall area − (doors × door area) − (windows × window area), plus the ceiling (length × width) if you paint it.
- Area to cover = paintable area × number of coats.
- Paint needed = area to cover ÷ coverage per gallon (or per liter).
Example: a 12 × 10 ft bedroom with 8 ft walls, one door and two windows, painted with two coats. The walls are 2 × (12 + 10) × 8 = 352 sq ft. Take off 21 sq ft for the door and 2 × 15 = 30 sq ft for the windows to get 301 sq ft. Two coats means 602 sq ft to cover, and at 350 sq ft per gallon that is 602 ÷ 350 = 1.72 gallons (6.5 liters). Rounded up to whole cans, you buy 2 gallons.
Typical paint coverage
Coverage is printed on the can and depends on the product and the surface. Rough, porous or patched walls soak up more paint, so use the lower end of the range for them.
| Product or surface | Per US gallon | Per liter |
|---|---|---|
| Interior wall paint, smooth drywall | 350–400 sq ft | 9–10 m² |
| Ceiling paint | 350–400 sq ft | 9–10 m² |
| Primer | 200–300 sq ft | 5–7.5 m² |
| Textured walls or stucco | 150–250 sq ft | 4–6 m² |
| Bare wood or new plaster | 250–300 sq ft | 6–7.5 m² |
| Exterior masonry paint | 200–300 sq ft | 5–7.5 m² |
Paint for common room sizes
Walls only, 8 ft (2.44 m) ceilings, one door, two windows, two coats at 350 sq ft per gallon.
| Room | Paintable walls | Paint needed | Buy |
|---|---|---|---|
| 8 × 10 ft (small bedroom) | 237 sq ft | 1.35 gal | 1 gallon + 2 quarts |
| 10 × 12 ft (bedroom) | 301 sq ft | 1.72 gal | 2 gallons |
| 12 × 14 ft (living room) | 365 sq ft | 2.09 gal | 2 gallons + 1 quart |
| 14 × 16 ft (large room) | 429 sq ft | 2.45 gal | 2 gallons + 2 quarts |
| 16 × 20 ft (open plan) | 525 sq ft | 3.00 gal | 3 gallons |
Gallons, quarts and liters
One US gallon is 3.785 liters and holds 4 quarts. Paint in the US is sold in quarts, gallons and 5-gallon buckets; three quarts usually cost about as much as a gallon, so the calculator rounds up to a full gallon in that case. In metric countries paint usually comes in 1 L, 2.5 L, 5 L and 10 L tins, and the calculator picks the combination of 1, 2.5 and 5 L tins with the least leftover paint. It is worth keeping a little extra for touch-ups.
Frequently asked questions
How much paint do I need for a 12 × 10 room?
With 8 ft walls, one door, two windows and two coats, the paintable wall area is 301 sq ft. Two coats is 602 sq ft, which at 350 sq ft per gallon is about 1.72 gallons, so buy 2 gallons.
How many square feet does a gallon of paint cover?
Most interior wall paints cover 350 to 400 sq ft per gallon on smooth, primed drywall. Textured or porous surfaces may only get 200 to 250 sq ft per gallon. Check the label on your can.
How many coats of paint do I need?
Two coats is standard for an even finish, especially when changing colour. One coat can be enough when refreshing the same colour, and a third coat may be needed for a dramatic change such as dark to light.
Should I subtract doors and windows?
Yes, for an accurate estimate. A standard interior door is about 21 sq ft (1.95 m²) and an average window about 15 sq ft (1.4 m²). The calculator takes these off the wall area, and you can change the sizes.
Do I need primer?
Primer is recommended on new drywall, bare wood, patched areas, glossy surfaces and when covering a dark colour. Tick the primer option to add one coat of primer to the estimate.
How much paint for a ceiling?
The ceiling area is simply length × width. A 12 × 10 ft ceiling is 120 sq ft, so two coats need about 240 ÷ 350 = 0.69 gallons. That is just under 3 quarts, so a single 1-gallon can is usually the better buy.