Paint Calculator
A 12 ft by 10 ft room with 8 ft walls, two windows and one door has 302 sq ft of wall to paint. Two coats at 350 sq ft per gallon take 1.73 gallons, so buy 1.75 to 2 gallons.
How to use
- Choose US units (feet, gallons) or metric (meters, liters).
- Enter the room length, width and wall height.
- Enter how many windows and doors there are and the size of each. Defaults are typical sizes.
- Set the number of coats and the coverage printed on your paint can. Tick Include ceiling if you are painting it too.
- Read the paint you need, and the amount to buy rounded up.
How it works
Wall area = 2 x (length + width) x height. Subtract the area of windows and doors. If you include the ceiling, add length x width.
Paint needed = net area x number of coats / coverage. For a 12 x 10 ft room with 8 ft walls, wall area is 2 x 22 x 8 = 352 sq ft. Two windows of 15 sq ft and a door of 20 sq ft take off 50 sq ft, leaving 302 sq ft. Two coats make 604 sq ft, and at 350 sq ft per gallon that is 1.73 gallons.
Coverage depends on the paint and the surface. Most cans list 250 to 400 sq ft per gallon (about 6 to 10 m² per liter). Rough, dark or porous walls soak up more, and new drywall usually needs a primer first. The tool rounds the buying amount up to the nearest 0.25 gallon or 0.5 liter, and it is wise to keep a little extra for touch-ups. It does not subtract baseboards, trim or closets, so those add a small margin.
Default sizes used
| Item | US units | Metric |
|---|---|---|
| Window | 15 sq ft | 1.4 m² |
| Door | 20 sq ft | 1.6 m² |
| Coverage | 350 sq ft per gallon | 10 m² per liter |
| Coats | 2 | 2 |
| Buying step | 0.25 gallon | 0.5 liter |
FAQ
How many coats of paint do I need?
Two coats is the usual advice. One coat can work over a similar color with a quality paint, and a big color change or bare drywall may need a primer plus two coats.
What coverage should I enter?
Use the figure on your paint can label. Typical values are 350 sq ft per US gallon (about 9 m² per liter) for interior wall paint, and many cans give a range of 250 to 400 sq ft.
Should I subtract windows and doors?
Yes for large ones. A standard door is about 20 sq ft (1.9 m²) and a typical window about 15 sq ft (1.4 m²). Small windows can be ignored if you want some spare paint.
Does it include trim and baseboards?
No. Trim usually takes a small separate amount, often a quart. Ceiling paint is a separate tick box because ceilings often use a different paint.