Paint Calculator
Work out how much paint a wall or a house needs, in litres or gallons, and which cans to buy.
Paint needed
- Area to paint
- Cans
An estimate. Porous surfaces soak up more, so round up rather than down.
Good to know
Finding the spread rate
Every can of paint states its spread rate (or coverage): how much surface one litre or one gallon covers on average. In metric it’s given as m²/l, in the US as square feet per gallon.
A spread rate of 6 m²/l means one litre covers 6 square metres, for example a 2 × 3 m area. A US can saying 350 sq ft/gal covers a 14 × 25 ft area with one gallon.
Typical spread rates:
- Matt interior wall paint: 8–12 m²/l (350–450 sq ft/gal)
- Exterior house paint: 5–8 m²/l (250–350 sq ft/gal)
- Primer: 7–10 m²/l (300–400 sq ft/gal)
- Masonry paint: 3–6 m²/l (150–250 sq ft/gal)
If you’re not sure how much the surface will soak up, use the smaller number, so you don’t run out halfway.
How much of the surface needs paint?
Windows and doors don’t need paint (at least if all goes well). For a wall with one normal-sized window, choose 75%. For a wall with a door and two windows, choose 50%. This is an estimate too, so round up rather than down.
How many coats?
Painting a light colour over a dark one indoors usually takes more than one coat. Depending on the surface, you may need a coat of primer first; calculate it separately with the primer’s own spread rate.
Which cans should I buy?
The calculator suggests the combination of standard cans (10, 5, 2.5 and 1 litre, or 5 gallons, 1 gallon and 1 quart) that leaves the least paint over. Bigger cans are usually cheaper per litre, so a little extra in one big can may cost less than several small ones. Can sizes vary by brand and country, so check what your store sells.
Happy painting!