Paint Calculator
Enter the length and height of your walls, take off doors and windows, and set the number of coats and the coverage printed on your paint can. The calculator returns the paint you need in gallons or liters, rounded up so you do not run short.
Last updated November 2, 2026
Distance around the room
On the paint can label
Result
Buy 3 gallons
2.09 gallons needed exactly, rounded up to a whole gallon.
| Wall area | 416 sq ft |
|---|---|
| Doors | −21 sq ft |
| Windows | −30 sq ft |
| Area to paint, one coat | 365 sq ft |
| Total area, 2 coats | 730 sq ft |
| Paint needed | 2.09 gallons |
Paint = wall area × coats ÷ coverage. Check the coverage printed on your can; it varies by paint and surface.
Show the work
Formula: paint = (wall area - doors - windows) x coats / coverage, rounded up to a whole unit
- Wall area: 52 x 8 = 416 sq ft.
- Doors and windows: 1 x 21 + 2 x 15 = 51 sq ft.
- Area to paint, one coat: 416 - 51 = 365 sq ft.
- All coats: 365 x 2 = 730 sq ft.
- Paint: 730 / 350 = 2.09 gallons, rounded up to 3 gallons.
Result: Buy 3 gallons
How the paint amount is worked out
paint = (length × height − doors − windows) × coats ÷ coverage
The wall area is the distance around the room times the wall height. For a 14 ft by 12 ft room, the distance around is 2 × (14 + 12) = 52 ft, and with 8 ft walls the area is 52 × 8 = 416 square feet. Doors and windows are not painted, so each one is taken off: a 3 ft by 7 ft door is 21 square feet and a 3 ft by 5 ft window is 15.
With one door and two windows, 416 − 21 − 30 = 365 square feet is left to paint. Two coats cover 730 square feet. Dividing by the coverage of the paint, 350 square feet per gallon, gives 730 ÷ 350 = 2.09 gallons. The calculator rounds up to whole gallons, so you would buy 3.
Metric works the same way with square meters and liters. A gallon is 3.785 liters, so 350 square feet per gallon is about 8.6 square meters per liter.
See how we calculate for the formulas, sources and review schedule behind every calculator.
Also useful alongside this calculator: Percentage Calculator, Length Converter and Ratio Calculator.
Coverage and the paint can
Coverage is how much area one unit of paint covers in a single coat, and it is printed on the can. Many labels quote 350 to 400 square feet per gallon, but it differs by brand and finish. The calculator starts at 350 and lets you enter your own number.
Rough or porous surfaces soak up more paint, so real coverage can be lower than the label, which makes the result larger. For the same 365 square feet and two coats, 300 square feet per gallon needs 2.43 gallons and 400 needs 1.83.
How many coats
Two coats are a common choice for an even finish, and a big color change may call for more. A single coat can be enough when repainting a similar color. Each extra coat adds the whole wall area again, so paint use rises in a straight line.
On the 365 square foot example at 350 square feet per gallon, one coat needs 1.04 gallons, two need 2.09 and three need 3.13. Primer is separate: it has its own coverage, so run the calculator again with the primer’s figure and one coat.
Doors, windows and what is not included
The sizes of 21 square feet for a door and 15 for a window are examples, not standards. Measure your own, or in metric use about 1.9 square meters for a door and 1.5 for a window. Setting the count to 0 ignores that opening, so you can leave its size as it is.
Ceilings, trim, skirting boards and cupboards are not included. To add a ceiling, multiply its length by its width and run the calculator again with that as one wall.
Imperial and metric units
Switching the unit setting converts everything you have entered, including the coverage. Values are rounded to two decimals, so re-enter measurements if you need exact figures.
How to use the Paint Calculator
- Choose imperial (feet, gallons) or metric (meters, liters).
- Enter the distance around the room and the wall height.
- Add the number of doors and windows and the area of one of each.
- Set the coverage from your paint can and the number of coats.
- Read the amount to buy, then use Copy, Print or Share.
Worked example
A 14 ft by 12 ft room has 52 ft of wall, 8 ft high, so 416 square feet. Take off one 21 square foot door and two 15 square foot windows to leave 365 square feet. Two coats make 730 square feet, and at 350 square feet per gallon that is 2.09 gallons, so buy 3. In metric, 16 m of wall that is 2.5 m high is 40 square meters; a 1.9 square meter door and two 1.5 square meter windows leave 35.1. Two coats at 10 square meters per liter need 7.02 liters, so buy 8.
| Coats | Total area (sq ft) | Gallons needed | Buy (gallons) |
|---|---|---|---|
| 1 | 365 | 1.04 | 2 |
| 2 | 730 | 2.09 | 3 |
| 3 | 1,095 | 3.13 | 4 |
Frequently asked questions
How much paint do I need for a 12 by 14 room?
With 8 ft walls, one door, two windows and two coats at 350 square feet per gallon, the room needs about 2.09 gallons, so buy 3.
Should I subtract doors and windows?
Yes, for a close estimate. In the example room, the door and windows remove 51 of 416 square feet.
How many square feet does a gallon of paint cover?
Labels often say about 350 to 400 square feet per coat. Check your can, because brand, finish and the surface all change the figure.
Does the result include ceilings, trim or primer?
No. It covers walls only. Add the ceiling area to the wall area, and run primer separately with its own coverage and one coat.
Are the figures exact, and is my data stored?
The result is an estimate based on the numbers you enter and the coverage you choose. Everything is calculated in your browser, and nothing you type is saved or uploaded.