Wall paint coverage: tins, coats and room measurements
Estimate paint from the surface you will actually coat, rather than the floor area of a room. This calculator accepts one wall's length and height in metres, the area of doors and windows in square metres, the number of coats and coverage in square metres per litre per coat. Repeat it for each wall and add the recommended litres. The 10 m²/L starting rate is a planning assumption, not a promise for every paint. Use the coverage printed on your chosen product's label; rough, porous or previously unpainted surfaces can require more paint.
Paint quantity formula
Paintable area = wall length × wall height − doors and windows area, with a minimum of zero. Paint needed = paintable area × coats ÷ coverage per litre per coat. Recommended buy = paint needed × 1.10, adding this calculator's fixed 10% allowance for roller loss, small mistakes and touch-ups. The allowance is a planning buffer, not a manufacturer's required rate.
Choose a positive coverage rate and a whole number of coats. Subtract each opening once from the wall area, not once per coat. A room's floor dimensions alone are insufficient: wall area also depends on ceiling height. For a rectangular room with equal-height walls, total wall area before openings is 2 × (room length + room width) × ceiling height. Paint the ceiling separately using room length × room width; include it only when using the same paint and coverage rate.
Litre tin coverage per coat
The table assumes 10 m²/L per coat and excludes the 10% allowance. One-coat coverage is tin litres × 10; the two-coat column is the surface area the same tin covers twice. If your label gives a different rate, replace 10 with that rate. A 2.5 litre tin therefore covers 25 m² once, or 12.5 m² twice, before losses.
| Tin size | One coat | Two coats |
|---|---|---|
| 1 L | 10 m² | 5 m² |
| 2.5 L | 25 m² | 12.5 m² |
| 5 L | 50 m² | 25 m² |
| 10 L | 100 m² | 50 m² |
US gallon coverage per coat
One US liquid gallon is exactly 3.785411784 litres. At the illustrative 10 m²/L rate, one US gallon covers about 37.85 m² for one coat, or 18.93 m² for two coats before allowance. This is a unit conversion of the example rate, not the coverage guarantee on a US paint label. A US gallon is not an imperial gallon.
| Container | One coat | Two coats |
|---|---|---|
| 1 US gal | 37.85 m² | 18.93 m² |
| 5 US gal | 189.27 m² | 94.64 m² |
Buying and preparing paint
Compare your recommended litres with the tin sizes actually available and round the purchase upward. The calculator's rounded cans result is only a count of 1 L equivalents; it is not a recommendation to buy that many individual tins. For example, 11.88 L could be covered by two 5 L tins plus one 2.5 L tin, giving 12.5 L in total. Availability varies by product and country.
Measure walls carefully, repair defects and follow the label's preparation, drying and recoat instructions. A major colour change or porous surface may need extra coats or primer. Calculate primer separately using its own coverage rate; do not assume a finish-paint estimate includes primer. Buy compatible paint in the same colour and finish, and retain its product and batch details for later touch-ups.
Worked examples
4 m × 5 m room, 3 m ceiling height
Assume four walls, a ceiling height of 3 m, no openings deducted, no ceiling painting, two coats and 10 m²/L per coat. Wall area = 2 × (4 + 5) × 3 = 54 m². Each 4 m wall needs 2.4 L and each 5 m wall needs 3 L for two coats. Total paint needed is 10.8 L; the 10% allowance gives 11.88 L. Two 5 L tins plus one 2.5 L tin supply 12.5 L. The ceiling would add 20 m² if painted, but is excluded here.
One wall with a window
A 4 m wall reaching a 3 m ceiling has 12 m² gross area. Subtract a 1.8 m² window to leave 10.2 m². With two coats at 10 m²/L, the calculator returns 2.04 L needed and 2.24 L recommended (2.244 L before display rounding). A 2.5 L tin exceeds that recommendation under these assumptions.
US gallon example: 12 ft × 15 ft room, 8 ft ceiling
Assume four walls, an 8 ft ceiling height, no openings and no ceiling painting. Wall area = 2 × (12 + 15) × 8 = 432 ft², or 40.13411328 m². For two coats at the illustrative 10 m²/L rate, paint needed is 8.026822656 L; adding 10% gives 8.8295049216 L, about 2.33 US gallons. Three 1 US gallon cans supply about 11.36 L. To reproduce this in the metric calculator, use 3.6576 m and 4.572 m for the two wall lengths, 2.4384 m height, zero openings and two coats; calculate each wall and sum the unrounded recommendations.
Frequently asked questions
How much does a 2.5 litre tin cover?
At 10 m²/L per coat, it covers 25 m² once or 12.5 m² twice before allowance. Including this calculator's 10% buffer, budget for about 22.73 m² once or 11.36 m² twice. Your paint label may specify a different coverage rate.
Does the coverage on a tin include two coats?
Check the label. When coverage is stated per coat, multiply your surface area by the number of coats before dividing by coverage. Do not treat one-coat coverage as the area a tin will finish with two coats.
Is ceiling paint included?
No. A wall estimate excludes the ceiling. Measure its length × width and calculate its coats separately, particularly if it uses a different paint.
Can I enter US gallons or feet directly?
The inputs use metres, square metres and m²/L. Convert feet to metres using 1 ft = 0.3048 m and convert US liquid gallons to litres using 1 US gal = 3.785411784 L. The US example above shows the same calculation in both systems.
Does the estimate include primer?
No. Estimate primer separately using the primer's stated coverage and number of coats. Follow the product's preparation instructions rather than assuming extra finish paint replaces primer.