Paint Calculator
Enter the room size, wall height, number of coats and the coverage from the paint can. The paint calculator gives the litres and US gallons you need, with a wastage allowance.
Paint calculator
Quantities are estimates. Real coverage depends on the surface, the paint and the application method. Read the label on the can.
Bare numbers are meters; 190 mm works too.
Bare numbers are meters; 190 mm works too.
Bare numbers are meters; 190 mm works too.
Most walls need 2 coats. Dark colours or new plaster may need more.
About 10 m²/L (107.6 sq ft/L, ~400 sq ft per US gallon) per coat; primer often covers less, 5–7 m²/L. Use the figure on your can.
Your price, any currency. Leave blank to skip.
Assumptions
Change any value to match your product or local rules.
Basis: Typical for cuts, touch-ups and the brush.
- Wall area
- 39.03 m²
- 420.1 sq ft
- Openings subtracted
- 3.09 m²
- 33.3 sq ft
- Paint needed
- 9.0 L
- Paint (US gallons)
- 2.38
- Cost (your currency)
- Add a price to see the cost
- Cost per m² of wall
- Add a price to see the cost
- Cost per sq ft of wall
- Add a price to see the cost
9 litres (2.38 US gal) of paint for 39.03 m², 2 coats with 10% added.
How this was calculated
- Wall area = perimeter × height − Σ (opening width × opening height × count)
- Paint = wall area × coats ÷ coverage per litre, rounded up
- US gallons = litres ÷ 3.785
- Cost per area = cost ÷ net wall area (paint only, no labour)
- Perimeter = 2 × (4.20 m + 3.60 m) = 15.60 m
- Gross wall area = 15.60 m × 2.70 m = 42.12 m²
- Opening 1 = 0.81 m × 2.03 m × 1 = 1.65 m²
- Opening 2 = 1.20 m × 1.20 m × 1 = 1.44 m²
- Net wall area = 42.12 m² − 3.09 m² = 39.03 m²
- Paint needed = 39.03 m² × 2 coats × 1.1 ÷ 10.00 m²/L = 8.6 L → 9 L
- US gallons = 8.6 L ÷ 3.785 = 2.38 US gal
How it works
Enter the walls
Room width and length, or list each wall. The calculator finds the perimeter and gross wall area.
Subtract the openings
Doors and windows are taken off automatically. Add any other openings you have.
Set the coats
Most walls need two coats. New plaster, a colour change or a rough surface may need more.
Read the paint
Litres needed with your wastage allowance, US gallons and, if you enter a price, the cost and the cost per m² and per sq ft of wall.
Worked example
A 4.2 × 3.6 m room with 2.7 m walls, one interior door (0.813 × 2.032 m) and one window (1.2 × 1.2 m). Perimeter = 15.6 m, gross wall area = 42.12 m². Openings: 1.652 + 1.44 = 3.092 m². Net wall area = 39.028 m². Two coats of emulsion at 10 m²/L with 10% added: 39.028 × 2 × 1.1 ÷ 10 = 8.586 L, so 9 litres (2.38 US gal).
In feet: a 14 × 12 ft room with 9 ft walls, one 3 × 7 ft door and one 4 × 4 ft window. Net area ≈ 431 sq ft. Two coats at 107.6 sq ft/L (the same 10 m²/L): 431 × 2 × 1.1 ÷ 107.6 = 8.81 L, so 9 litres (2.38 US gal).
Coverage per litre
The calculator starts at 10 m²/L per coat (107.6 sq ft/L, about 400 sq ft per US gallon). Sherwin-Williams says a gallon of paint typically covers about 350–400 sq ft (9.2–10.6 m²/L), and that a gallon of primer covers about 200–300 sq ft (4.9–7.4 m²/L), so primer covers less than topcoat. Labels vary: some emulsions quote more per litre on a smooth, sealed wall. Rough surfaces, new plaster and absorbent backgrounds take more paint. The figure on the can is the maker's own test result, so use that when you have it.
How many coats
Two coats is the standard for a colour that is not a big change from what is there. New plaster needs a sealer or mist coat first, then two coats of topcoat. A dark colour over a light one may need three. The calculator lets you set any number.
Wastage allowance
The 10% default covers the paint left in the tray, the brush and roller, and touch-ups after drying. A rough surface or a textured finish may need more. Roller nap thickness, surface texture and application method all change the real coverage.
Frequently asked questions
How many litres of paint do I need per m²?
Many emulsions cover about 10 m² per litre per coat (Sherwin-Williams: 350–400 sq ft per US gallon, 9.2–10.6 m²/L); your can gives the exact figure. Multiply the wall area by the number of coats, divide by the coverage per litre and add a wastage allowance.
How do I calculate paint for a room?
Wall area = perimeter × height − doors − windows. Then: litres = wall area × coats ÷ coverage per litre. A 4.2 × 3.6 m room with 2.7 m walls, one door and one window takes about 9 litres for two coats of emulsion at 10 m²/L.
How many US gallons is that?
1 US gallon = 3.785 litres. Divide the litres by 3.785. Nine litres is about 2.38 US gal.
What does paint cost per square metre of wall?
Divide the paint cost by the net wall area. A 4 × 3 m room with 2.5 m walls and no openings has 35 m² of wall; two coats at 10 m²/L with 10% added need 8 litres, which at 12 per litre is 96, or 2.74 per m² (0.25 per sq ft). That is paint only, with no labour.
Does wall texture change the paint needed?
Yes. Rough or textured walls take more paint. Raise the wastage allowance or use the lower end of the coverage range if your surface is rough.
Do I subtract doors and windows from the paint area?
Yes. The calculator subtracts every opening you enter from the gross wall area, giving the net area you need to cover.
Ready to plan your space?
It is free, runs in your browser and needs no account. Projects are saved privately on this device.