Paint calculator
EverydayHow much paint do I need for a room?
Litres or gallons of paint and whole cans to buy, from the room's size, the coats and the coverage on the tin.
What you enter stays on your device while you use this tool. Opening a shared link sends the settings in its address to HowToolbox to prepare the page.
Ceiling, openings and tin
Their total area, width × height each; leave 0 to paint over them.
Use the figure on the tin: about 10 m² per litre (400 ft² per gallon) is typical for wall paint on a smooth surface; rough or bare walls take more.
Paint needed
7 L
Buy 3 cans of 2.7 L · 35 m² to paint, 2 coats
Areas and cans
- Walls
- 35 m²
- Paint in the cans
- 8.1 L
- Left over for touch-ups
- 1.1 L
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Litres or gallons of paint and whole cans to buy, from the room's size, the coats and the coverage on the tin.
How to use
- Enter the room's length, width and wall height, and the number of coats.
- Below, add the ceiling, the doors and windows to leave out, the coverage printed on your tin and the can size.
- Read the paint needed and how many whole cans to buy.
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How it works
The walls of a box-shaped room are two pairs of rectangles, so their area is 2 × (length + width) × height. Take off the doors and windows you won't paint, multiply by the number of coats and divide by the coverage: how many square metres one litre covers in one coat. Then round up to whole cans.
Coverage depends on the paint and the surface, so the figure on your tin is the one to trust: around 10 m² per litre, or 400 square feet per US gallon, is typical for wall paint on smooth, primed walls. Bare plaster, rough or porous surfaces and big colour changes take more paint or an extra coat. The room is treated as a simple box; add alcoves and sloping walls separately.
Worked example
How much paint for a 4 × 3 m room with 2.5 m walls?
- 2 × (4 + 3) × 2.5 = 35 m².
- 35 × 2 ÷ 10 = 7 L.
With no openings or ceiling, buy 3 cans of 2.7 L for 2 coats.
Frequently asked questions
Do I really need two coats?
Usually, yes: one coat rarely hides the old colour evenly. A primer and one coat can do on new plaster, and a strong colour change may need three.
Should I subtract doors and windows?
Subtract the big ones, such as patio doors and large windows. Small ones make little difference and the spare paint covers mistakes.
How much paint for the ceiling?
Switch on the ceiling: it adds length × width. Ceilings often use a different paint, so you can also work them out separately with that tin's coverage.
Where do I find the coverage?
On the tin or the product sheet, often as square metres per litre (m²/L) or square feet per gallon. Use the lower number if a range is given.
Can I buy fewer, larger cans?
Yes. Change the can size to compare the number of cans and leftover paint; the litres needed stay the same.
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