Paint Coverage Calculator
Estimate how much paint a room needs from its wall dimensions or total wall area, the number of coats, the coverage rate and any openings. Measure in metric or imperial and buy in litres or US gallons — the two choices are independent.
Covers 2 coats. Includes a 10% waste allowance. The suggested pack holds 7.5 L altogether.
Paint coverage is approximate. Spreading rate varies with the paint, the surface and its porosity, the size of the colour change and how the paint is applied. Keep a little spare for touch-ups.
Check the openings
How to use this calculator
- Set Measurement units to Metric or Imperial. This controls how you enter the room and whether the area reads in m² or ft². Switching converts what you have entered.
- Set Paint purchase units to Litres or US gallons — how the paint is sold where you are buying it. This can differ from your measurement units.
- Choose Room dimensions to enter length, width and wall height, or Direct wall area if you already know the total.
- Enter the number of doors and windows to subtract, and choose the number of coats.
- Set the coverage rate from the tin or can, and a waste allowance.
- Read the paint to buy, the paintable area, and a suggested combination of tins or cans.
How is paint coverage calculated?
The calculator finds the wall area, subtracts the openings, multiplies by the number of coats, then divides by the coverage rate and adds the waste allowance.
- opening area = (doors × 2.0 m²) + (windows × 1.5 m²)
- net wall area = gross wall area − opening area
- paintable area = net wall area × coats
- paint needed = paintable area ÷ coverage rate
- paint to buy = paint needed × (1 + waste ÷ 100)
When you buy in litres, the calculator divides the paintable area in square metres by the coverage in m² per litre. When you buy in US gallons, it converts the area to square feet and divides by the coverage in ft² per US gallon. The measurement units only change how the room is entered and how the area is displayed — the paint result always follows your purchase units. Each purchase unit keeps its own default coverage; 10 m² per litre is not simply converted into 400 ft² per US gallon.
Example: a 4 m × 3 m room with 2.4 m walls, one door and two windows, bought in litres
- 2 × (4 + 3) × 2.4 = 33.6 m² of wall.
- (1 × 2.0) + (2 × 1.5) = 5.0 m² of openings, so 28.6 m² of net wall area.
- 28.6 × 2 coats = 57.2 m² to cover.
- 57.2 ÷ 10 = 5.72 litres, and with a 10% allowance, 6.3 litres.
- The best fit from whole tins is one 5 L tin plus one 2.5 L tin.
Same room measured in feet, bought in US gallons: 13 ft × 10 ft × 8 ft walls
- 2 × (13 + 10) × 8 = 368 ft² of wall, less about 53.8 ft² of openings ≈ 314 ft².
- 314 × 2 coats ≈ 628 ft² to cover.
- 628 ÷ 400 = 1.57 US gallons, and with a 10% allowance, about 1.7 US gallons.
- The best fit from whole cans is one 2 gallon can.
Measured in feet, bought in litres: the area is shown in ft² with the m² equivalent beside it, the coverage rate stays in m² per litre, and the result is in litres.
Paint coverage rates by type
Coverage, or spreading rate, is the area one litre covers in a single coat. Always use the figure on your tin where you have it; the ranges below are typical starting points.
| Paint type | Typical coverage |
|---|---|
| Emulsion (matt or silk) | 10–12 m² per litre |
| Primer or undercoat | 8–10 m² per litre |
| Gloss or satinwood | 12–14 m² per litre |
| Masonry paint | 6–10 m² per litre |
| Wood stain | 15–25 m² per litre |
Bare plaster, new filler and porous surfaces absorb more paint, so the first coat covers less than the second. A mist coat of watered-down emulsion on new plaster spreads further.
Paint tin and can sizes
With litres selected, the calculator rounds your requirement up to the next half-litre and suggests a mix of 10 L, 5 L, 2.5 L and 1 L tins. With US gallons selected, it rounds up to the next quarter-gallon (one quart) and suggests a mix of 5 gal, 2 gal, 1 gal and 1 qt cans. Either way it balances the paint left over against the number of containers, so a job just under a container size rounds up to that size rather than being split across several small ones.
| Tin size | Rough one-coat coverage |
|---|---|
| 5 L | About 50–60 m² in one coat of emulsion |
| 2.5 L | About 25–30 m² in one coat of emulsion |
| 1 L | About 10–12 m² in one coat of emulsion |
Buying one larger tin is usually cheaper per litre than several small ones, and keeping a little spare from the same batch makes future touch-ups an exact colour match.
Do my measuring units have to match my paint units?
No. Your measuring units do not need to match the units used to buy paint. For example, you can measure a room in feet and inches but calculate the paint needed in litres. The calculator converts every dimension into one internal area in square metres, so the two choices stay independent and switching either one keeps the real room size.
Measurement units control the room entry and the area display:
| Setting | Metric | Imperial |
|---|---|---|
| Room dimensions | Metres, centimetres, millimetres | Feet and inches |
| Area shown as | m² | ft² |
Paint purchase units control the coverage rate, the result and the containers:
| Setting | Litres | US gallons |
|---|---|---|
| Paint result | Litres (L) | US gallons (US gal) |
| Coverage rate | m² per litre | ft² per US gallon |
| Typical default coverage | 10 m² per litre | 400 ft² per US gallon |
| Container sizes | 1 L, 2.5 L, 5 L, 10 L | 1 qt, 1 gal, 2 gal, 5 gal |
When the two systems differ, the paintable area is shown in your measurement units with the coverage-rate unit beside it, so you can see the figure that feeds the calculation. Coverage depends on the paint product, surface condition, colour change, texture and number of coats — always check the coverage stated on the specific product before buying.
How accurate is this estimate?
This is a guide, not an exact figure. Real usage depends on the paint, the surface and its porosity, the size of the colour change, the roller or brush, and how thickly the paint is applied. Treat the result as a minimum to buy, and keep the waste allowance for the surfaces that drink paint.