Paint Calculator

How much paint you need for a room: walls and ceilings less doors and windows, any number of coats, in gallons or litres, and which tins to buy.

Paint is worked out from the area you're covering, the number of coats and the coverage on the tin. A 12 × 10 ft room with 8 ft walls has 44 ft of wall, so 352 ft² of wall; take off a door (about 20 ft²) and a window (12 ft²) and you're painting 320 ft². Two coats at 350 ft² per gallon is 1.83 gallons. In metric, a 4 × 3 m room 2.4 m high is 33.6 m² of wall, about 30.5 m² after a door and a window, so two coats at 12 m² per litre is just over 5 litres. Enter your rooms or individual walls, the doors and windows, and the coats, and this calculator gives the paint needed and the mix of tins to buy: quarts, gallons and 5-gallon pails in the US, or 1, 2.5, 5 and 10 litre tins in the UK and 1, 4, 10 and 15 litre tins in Australia.

Units
Bag sizes
Measure by
Room
ft
ft
ft
Feet and inches work too: type 12'6 or 12.5.
Doors and windows to leave out
ft
ft
ft
ft
%
Paint needed
2.01 gal

7.61 litres

Buy
2 × 1 gallon + 1 × quart

2.25 gal in 3 tins

Area to paint
320 ft²

2 coats

How it was worked out
  1. Walls: 2 × (12 + 10 ft) = 44 ft around × 8 ft high = 352 ft²
  2. Less 1 door (20 ft²) and 1 window (12 ft²) = −32 ft²
  3. Area to cover: 320 ft²
  4. 320 ft² × 2 coats ÷ 350 ft² per gallon = 1.83 gal
  5. Plus 10% extra = 2.01 gal
  6. Tins: 2 × 1 gallon + 1 × quart = 2.25 gal

Coverage is for one coat on smooth, sealed walls; the figure on your tin is the one to use. New plaster, bare wood, rough or porous surfaces and big colour changes take more paint, or a primer first.

Common use cases

  • Buy the right amount of paint for a bedroom, living room or whole house
  • Work out ceiling paint as well as wall paint
  • Check whether a 2.5 L or 5 L tin (or a gallon or 5-gallon pail) is enough
  • Paint a single feature wall or a fence panel by entering walls instead of rooms

How to use

  1. Choose your units and which country's tin sizes you want.
  2. Enter each room's length, width and wall height, or switch to Wall and enter walls one by one.
  3. Enter the doors and windows to leave out, and tick Include ceilings if you're painting them.
  4. Set the coats and the coverage from your tin, then read the paint needed and the tins to buy.

FAQ

How much does a gallon or a litre of paint cover?

Most US interior paints say about 350 to 400 ft² per gallon for one coat. Most UK and Australian interior paints say somewhere between 10 and 16 m² per litre. Rough, porous or new surfaces take more, so use the figure on your tin and treat it as a best case.

How many coats of paint do I need?

Two coats is the usual answer for walls, especially when changing colour. A big change from dark to light, new plaster or new drywall often needs a primer or mist coat first, and some deep colours need a third coat.

Should I take off doors and windows?

Yes for anything sizeable. A standard door is about 20 ft² (about 1.7 m²), so in a small room it makes a real difference. Small openings can be ignored; the extra allowance covers them.

How much paint for a ceiling?

The ceiling of a room is its length times its width: a 12 × 10 ft ceiling is 120 ft², roughly a third of a gallon per coat at 350 ft² per gallon. Tick Include ceilings and the calculator adds it.

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