Paint Calculator
Estimate how much paint to buy for a room or wall, with doors, windows, ceiling, coats and primer, in gallons or liters.
Results
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Paint needed
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Cans to buy
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Area to paint
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Estimated cost
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Breakdown
How it's worked out
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How to use the paint calculator
- Choose "Room size" to measure a whole room, or "Wall area" if you already know the area.
- For a room, enter its length, width and wall height, and how many doors and windows it has. The standard sizes can be changed.
- Tick "Also paint the ceiling" to include it. The ceiling amount is shown separately.
- Set the number of coats and the coverage printed on your paint can, then read how many gallons or liters to buy.
How the paint is calculated
The wall area of a rectangular room is its perimeter times the wall height:
Wall area = 2 × (length + width) × height
Doors and windows are taken off, and the ceiling (length × width) is added if you include it. Then:
Paint = area to paint × coats ÷ coverage per gallon (or liter)
In US units the result is rounded up to whole gallons plus quarts. When three or more quarts would be needed, the calculator suggests another gallon instead, because it usually costs about the same. In metric units it suggests the common 5 L, 2.5 L and 1 L tin sizes.
Worked example
A 12 × 10 ft bedroom with 8 ft walls, one door, two windows and two coats, including the ceiling:
- Walls: 2 × (12 + 10) × 8 = 352 ft².
- Openings: 20 + 2 × 15 = 50 ft², leaving 302 ft² of wall.
- Wall paint: 302 × 2 coats ÷ 350 = 1.73 gallons, so buy 2 gallons.
- Ceiling: 12 × 10 = 120 ft² × 2 coats ÷ 350 = 0.69 gallons, so 1 gallon of ceiling paint.
Paint for common room sizes
Two coats, 8 ft walls, one door and one window, 350 ft² per gallon:
| Room | Wall area | Walls | Ceiling |
|---|---|---|---|
| 10 × 10 ft | 285 ft² | 2 gallons | 1 gallon |
| 12 × 12 ft | 349 ft² | 2 gallons | 1 gallon |
| 12 × 14 ft | 381 ft² | 2 gallons + 1 quart | 1 gallon |
| 14 × 16 ft | 445 ft² | 3 gallons | 1 gallon + 2 quarts |
| 16 × 20 ft | 541 ft² | 3 gallons + 1 quart | 2 gallons |
One US gallon is 3.785 liters and holds 4 quarts.
Frequently asked questions
How much paint do I need for a 12 × 12 room?
A 12 × 12 ft room with 8 ft walls has 384 square feet of wall. Take off one door (about 20 sq ft) and one window (about 15 sq ft) and you have 349 sq ft. Two coats at 350 sq ft per gallon need 1.99 gallons, so buy 2 gallons for the walls, plus about 1 gallon if you are painting the ceiling too.
How many coats of paint do I need?
Two coats is the usual answer for walls: the first coat evens out the surface and the second gives full, even color. One coat can be enough when repainting the same color with a good-quality paint. Large color changes, especially light over dark, may need three coats or a primer first.
How much does a gallon of paint cover?
Most interior wall paints state about 350 to 400 square feet per gallon for one coat on a smooth, primed surface, which is roughly 8.5 to 10 square meters per liter. Rough, porous or textured surfaces soak up more, so coverage can drop to 250 square feet per gallon or less. Use the figure printed on your can.
Do I need a primer?
Use a primer on new drywall, bare wood, patched areas, glossy surfaces and stains, and when covering a much darker color. Tick "Add a primer coat" to estimate one coat of primer over the same area.
Can I use wall paint on the ceiling?
You can, but ceiling paint is usually flat, thicker and designed to spatter less when rolled overhead. The calculator shows the ceiling amount separately so you can buy it as a different product.