Paint Calculator (Litres, Gallons & Cans)
Estimate how much interior paint and primer you need in litres, US gallons, and cans to coat the walls and ceiling of a room, from its dimensions, coats, and paint coverage.
Paintable area 36.5 m² per coat (walls 40.5 m²), 2 coats at 11 m²/L. Trim, doors, and frames are painted separately.
How this works
Paint volume is the paintable area times the number of coats, divided by the coverage (spread rate):
wall area = 2 × (L + W) × H
net = (wall + ceiling) × (1 − openings%)
litres = net × coats / coverage × (1 + waste%)
gallons = litres / 3.785
cans = ceil(litres / can size)Typical interior emulsion covers about 11 m² per litre per coat (350–400 ft² per US gallon) on a smooth sealed surface; bare or textured surfaces cover less.
Worked example
A 4 m × 3.5 m room, 2.7 m high, walls only, 10% openings, 2 coats at 11 m²/L, 5% waste:
- walls =
2 × 7.5 × 2.7= 40.5 m²; net =× 0.90≈ 36.45 m² - litres =
36.45 × 2 / 11 × 1.05≈ 6.96 L (≈ 1.84 US gal) - cans =
ceil(6.96 / 5)= 2 × 5 L cans; 1 primer coat ≈ 3.5 L
Sources
- Coverage rates are typical emulsion/latex spread rates; always use the spread rate printed on your specific paint.
FAQ
How do I calculate how much paint I need?
Work out the surface area (the wall perimeter times the height, plus the ceiling if you are painting it), deduct a percentage for doors and windows, multiply by the number of coats, then divide by the paint's spread rate. For example, 40 m² of wall over two coats at 11 m² per litre needs about 40 × 2 ÷ 11 = 7.3 litres. This calculator does all of that and also converts the result to US gallons and to a can count.
How much area does a litre or gallon of paint cover?
A litre of standard interior emulsion covers roughly 10 to 13 m² per coat on a smooth, sealed surface, so a typical figure is about 11 m² per litre. One US gallon (3.785 litres) covers roughly 350 to 400 square feet per coat. Rough, textured, or very porous surfaces such as bare plaster or masonry absorb more and cover less, so drop the coverage figure for those. Always check the spread rate printed on your specific product's tin.
How many coats of paint do I need?
Two finish coats is the standard for a durable, even colour on most interior walls. You may need three when going from a dark colour to a light one, when using strong or translucent colours like deep reds and yellows, or over a patchy repair. New or bare surfaces should also get a primer or sealer coat first, which this calculator can add separately so it does not distort the finish-paint figure.
Do I need primer, and how much?
Prime bare plaster, new drywall, filler and repairs, glossy or previously oil-painted surfaces, and any big colour change. Primer seals porous surfaces so the finish coats cover evenly, which can actually reduce the number of finish coats you need. One primer coat is usually enough; set the primer coats field to 1 (or 2 for very porous walls) and the calculator estimates primer litres using the same coverage rate as a starting point.
Should I subtract doors and windows?
For a room with one door and a window, you can leave the openings deduction at zero and let the small over-estimate act as a buffer. For rooms with large windows, sliding doors, or several openings, deducting 10 to 15 percent of the gross wall area gives a tighter estimate and avoids buying an extra tin you do not use. Remember trim, frames, and doors themselves may need their own paint, counted separately.
Why does the calculator show both litres and gallons?
Paint is sold in litres across most of the world (Australia, the UK, Europe, and Asia) and in US gallons and quarts in the United States. Showing both, along with a can count for the tin size you pick, means you can order the right number of containers wherever you are buying. One US gallon is 3.785 litres; one imperial gallon (rarely used for paint now) is 4.546 litres.