Paint Coverage Calculator

How to use this calculator

1. 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.
2. 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.
3. Choose Room dimensions to enter length, width and wall height, or Direct wall area if you already know the total.
4. Enter the number of doors and windows to subtract, and choose the number of coats.
5. Set the coverage rate from the tin or can, and a waste allowance.
6. Read the paint to buy, the paintable area, and a suggested combination of tins or cans.

What do I need to enter?

• Measurement units — Metric or Imperial, for entering the room and reading the area. Paint purchase units — Litres or US gallons, for the coverage rate and the result.
• Room length, Room width and Wall height — each above zero and up to 100 m, in m, cm, mm, ft or in. Used with Room dimensions.
• Total wall area — above zero and up to 100,000 m². Used instead of the dimensions with Direct wall area.
• Doors and Windows — whole numbers up to 999, blank for none. Each door takes off 2.0 m² and each window 1.5 m².
• Number of coats — 1, 2 or 3.
• Coverage rate — the area one litre or US gallon covers in one coat, from the tin. It must be above zero, up to 100 m² per litre or 4,000 ft² per US gallon.
• Waste allowance — 0%, 5%, 10% or 15% extra for touch-ups and paint left in the tin.

What do the results show?

• Paint to buy — the main figure, in litres or US gallons, including the waste allowance.
• Paintable area — wall area minus openings, multiplied by the coats. A second figure gives it in the coverage rate's units when they differ from your measurement units.
• Coverage rate and Coats — the values the result used.
• Suggested tins or cans — a combination of whole containers that covers the amount, with the total volume it holds.
• Check the openings — shown instead of a result when the doors and windows take up all of the wall area.

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.

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

1. 2 × (4 + 3) × 2.4 = 33.6 m² of wall.
2. (1 × 2.0) + (2 × 1.5) = 5.0 m² of openings, so 28.6 m² of net wall area.
3. 28.6 × 2 coats = 57.2 m² to cover.
4. 57.2 ÷ 10 = 5.72 litres, and with a 10% allowance, 6.3 litres.
5. 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

1. 2 × (13 + 10) × 8 = 368 ft² of wall, less about 53.8 ft² of openings ≈ 314 ft².
2. 314 × 2 coats ≈ 628 ft² to cover.
3. 628 ÷ 400 = 1.57 US gallons, and with a 10% allowance, about 1.7 US gallons.
4. 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.

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.

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:

Paint purchase units control the coverage rate, the result and the containers:

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.

Related tools

Tiling part of the wall rather than painting all of it? See the Tile Calculator.

Frequently asked questions