Paint Calculator
- Free forever
- No sign-up
- Runs in your browser
Work out how much paint you need for a room from the wall size, doors, windows and number of coats, in litres or US gallons.
Walls of different lengths? Add them up and enter the total as one wall. For a ceiling, enter its length and width as one wall.
How it’s calculated
- Wall area = wall length × height × number of walls.
- Area to paint = wall area − doors − windows.
- Paint = area to paint × coats ÷ coverage. 1 US gallon = 3.785 litres.
Example: four 12 × 8 ft walls are 384 sq ft. Take off a door (21 sq ft) and a window (15 sq ft) to get 348 sq ft. Two coats make 696 sq ft, and 696 ÷ 350 sq ft per gallon = 1.99 gallons, so two 1-gallon cans.
In metric: four 3.6 × 2.4 m walls are 34.56 m². Minus a 1.9 m² door and a 1.4 m² window, that’s 31.26 m². Two coats make 62.52 m², and 62.52 ÷ 9 m² per litre = 6.9 litres: a 5 litre tin and two 1 litre tins.
About Paint Calculator
Measure your walls, count the doors and windows, choose the number of coats and type in the coverage from the tin. You get the area to paint, the paint you need in litres and US gallons, and a suggested set of tins with the least paint left over. It also works for a ceiling: enter its length and width as a single wall.
How to use Paint Calculator
- Choose your units and the number of coats.
- Enter the wall length and height and the number of walls. For walls of different lengths, add the lengths and enter them as one wall.
- Enter how many doors and windows there are and the size of each, then the coverage printed on your tin.
- Read the area to paint, the litres and US gallons you need, and the suggested tins.
How your data is handled
Everything is worked out in your browser as you type. Nothing you enter is sent or saved, apart from your choice of metric or imperial units, which is remembered on your device.
Limits and accuracy
- Tin coverage figures are for smooth, sound walls. Rough plaster, bare wood and new drywall soak up more, and a primer coat isn't included.
- Tin suggestions use 5 gallon, 1 gallon and quart sizes, or 5, 2.5 and 1 litre tins. Your shop's sizes may differ.
- It's for walls and ceilings. Doors, trim and window frames need a separate, smaller amount of paint.
Questions and answers
How much paint do I need for a room?
Add up the wall area (length × height for each wall), take off the doors and windows, multiply by the number of coats and divide by the coverage on the tin. Four 12 × 8 ft walls with one door and one window come to 348 sq ft. Two coats at 350 sq ft per gallon need about 2 gallons.
How much does a gallon of paint cover?
Sherwin-Williams says a gallon typically covers about 350 to 400 square feet, and Behr gives 250 to 400 sq ft for one coat of its interior paints. That's roughly 6 to 10 m² per litre. Rough, porous and new surfaces take more.
How many coats of paint do I need?
Two coats is the usual choice for an even finish, and it matters most when you change colour a lot. One coat can be enough when you repaint in a similar colour, so check the instructions on the tin.
How much should I take off for doors and windows?
Measure yours if you can. As a starting point the calculator uses 21 sq ft for a door (about 3 × 7 ft) and 15 sq ft for a window (about 3 × 5 ft), or 1.9 m² and 1.4 m² in metric. Change the sizes to match your room.
How many litres of paint do I need for a room?
Four 3.6 × 2.4 m walls with one door and one window leave 31.3 m² to paint. Two coats at 9 m² per litre need about 6.9 litres, so a 5 litre tin and two 1 litre tins.
Does it include the ceiling?
Not by default. For a ceiling, enter its length as the wall length, its width as the height and 1 as the number of walls, with no doors or windows, and add the result. Ceiling paint can have a different coverage, so check its tin.
Litres or gallons?
Both are shown. One US gallon is 3.785 litres. The UK and many other countries sell paint in litres, in tins such as 1, 2.5 and 5 litres.