Find out how much wall paint to buy for a room. Enter the room size, wall height and number of doors and windows, and the calculator gives you the paint in gallons or litres, the number of cans or tins and the cost.
Your shopping list
How to measure
- Measure the length and width of the room and the height of the walls.
- Count the doors and windows. We subtract a standard size for each one.
- Check the coverage on the tin. Most wall paints cover 10–12 m² per litre, or about 350–400 sq ft per gallon.
The formula
Wall area = 2 × (length + width) × height − doors − windows Paint = wall area × coats ÷ coverage
Worked example
A 12 × 12 ft room with 8 ft walls has 384 sq ft of wall. Minus one door and two windows leaves 333 sq ft. Two coats at 350 sq ft per gallon need 1.9 gallons, so buy 2 cans.
Tips before you buy
- New plaster or drywall soaks up paint. Use a primer or a thinned mist coat first.
- Dark colours over light walls, and light over dark, often need a third coat.
- Buy all the paint at once and mix the tins together for an even colour.
Frequently asked questions
Do I need two coats?
Usually yes, especially when changing colour or painting fresh plaster or drywall.
How much paint for a ceiling?
Multiply the room length by the width and divide by the coverage of your ceiling paint. Add a second coat if needed.
How much does a gallon of paint cover?
About 350–400 sq ft per coat on smooth walls. Textured or porous surfaces use more.
Results are estimates for planning only. Always check quantities with your supplier before you buy.