Paint calculator: litres, US gallons and whole cans of paint and primer for a room, from wall area minus doors and windows, coats and coverage.
By AdminDrafted with AI writing toolsUpdated Checked examples: 5
36.9 m² (397 ft²) to paint × 2 coats needs 7.38 L (1.95 US gal), so buy 2 × 5 L cans.
Rounded up to whole 5 L cans.
Paint needed is the area to cover times the number of coats, divided by the coverage printed on the can. Wall area is the room's perimeter times the wall height, 2(length + width) × height, plus the ceiling if you include it, minus each door and window. The result is rounded up to whole cans of the size you pick.
The default 4.5 × 3.5 m room with 2.6 m walls, one door and two windows leaves 36.9 m² to paint. Two coats at 10 m² per litre need 7.38 L, which is two 5 L cans. For US paint, switch coverage to ft² per gallon; Sherwin-Williams puts a gallon at about 350–400 ft² per coat.
Label coverage assumes a smooth, sealed surface. Bare plaster, rough texture and strong colour changes use more paint, so treat the answer as the minimum to buy.
For walls, ceilings or any flat surface, multiply the area by the number of coats and divide by the coverage per coat. A 12 × 10 ft room with 8 ft walls, a door and two windows has 308 ft² of wall; two coats at 350 ft² per gallon take 1.76 gallons, or two cans.
Metric rooms work the same way. A 4.5 × 3.5 m room with 2.6 m walls has 41.6 m² of wall, or 36.9 m² after a 1.9 m² door and two 1.4 m² windows. Two coats at 10 m² per liter need 7.38 L, or two 5 L cans.
Add the ceiling (length × width) only if it gets the same paint. Here it adds 15.75 m², which raises the total to 52.65 m² and 10.53 L, or three 5 L cans.
Dulux's estimating guide follows the same steps: measure each wall, deduct doors and windows, then divide by the coverage once for every coat.
Sherwin-Williams puts a gallon of interior paint at about 350–400 ft² per coat, and a gallon of primer at 200–300 ft². Wall paints sold by the liter typically cover 10–16 m² per liter on a smooth surface.
Convert before comparing a US label with a metric one: 350 ft² per US gallon is only 8.6 m² per liter, while 10 m² per liter is about 407 ft² per gallon.
Coverage drops on bare plaster, rough texture and strong color changes. Use the label's figure for that surface, or the low end of its range when it gives one.
Primer is one coat at its own coverage rate, usually lower than the paint's. The 36.9 m² room at 8 m² per liter needs 4.61 L of primer, one 5 L can on top of the 7.38 L of paint.
The first four rows are the 4.5 × 3.5 m room above, painted from 5 L cans, with one change each. "Primer own rate" adds the 8 m² per liter primer coat, which leaves the paint figures unchanged.
"US room" is the 12 × 10 ft room converted to metric: 308 ft² is 28.61 m², and 1.76 gallons is 6.66 L, still two 1-gallon cans.
| Scenario | Net area, m² | Finishing paint, L | Paint cans |
|---|---|---|---|
| Default | 36.900000 | 7.380000 | 2.000000 |
| Ceiling included | 52.650000 | 10.530000 | 3.000000 |
| One coat | 36.900000 | 3.690000 | 1.000000 |
| Primer own rate | 36.900000 | 7.380000 | 2.000000 |
| US room | 28.614136 | 6.662325 | 2.000000 |
For an L-shaped room, get the wall area from the room area calculator. Wallpaper and drywall start from the same wall measurement: see the wallpaper calculator and the drywall calculator.
Checked against: 2(4.5 + 3.5) × 2.6 − 1.9 − 2 × 1.4 = 36.9 m²; × 2 ÷ 10 = 7.38 L; 7.38 ÷ 5 → 2 cans
Checked against: Hand calculation: 4 × 12 × 8 = 384 ft² − 20 − 30 = 334 ft²; 668 ÷ 350 = 1.9086 gal → 2 one-gallon cans
Checked against: 45 m² walls + 20 m² ceiling; 130 ÷ 10 = 13 L → 5.2 → 6 cans; primer 6.5 L → 2.6 → 3 cans
Checked against: 334 ft² ÷ 250 ft²/gal = 1.336 gal × 3.785411784 L = 5.0573 L → 2 one-gallon cans
About 2 US gallons for two coats on the walls. A 12 × 12 ft room with 8 ft walls has 384 ft² of wall; less one 20 ft² door and two 15 ft² windows, 334 ft² remains. Two coats is 668 ft², which at 350 ft² per gallon is 1.91 gallons. Painting the 144 ft² ceiling as well raises the total to 2.73 gallons.
About 350–400 ft² per coat, according to Sherwin-Williams, and a quart covers about 100 ft². In metric, 350–400 ft² per US gallon is 8.6–9.8 m² per litre. Use the figure printed on your own can, because coverage changes with the product, the colour and the surface.
Two for most walls. Dulux's guide gives one coat for its Simply Refresh one-coat range and two for EasyCare Washable & Tough. Every coat adds the full area again: the default 36.9 m² room needs 3.69 L per coat at 10 m² per litre, so a third coat adds another 3.69 L.
Yes. Dulux's method measures each wall as height × width and deducts doors and windows measured the same way. This calculator uses 1.9 m² (20 ft²) per door and 1.4 m² (15 ft²) per window unless you enter your own sizes under More options. In the default room the three openings remove 4.7 m², 11% of the 41.6 m² of wall.
One coat over the whole area, at the primer's own coverage rate. Sherwin-Williams gives about 200–300 ft² per gallon for primer against 350–400 ft² for paint, so 334 ft² of wall takes 1.1–1.7 gallons of primer. Enter the primer label's figure as Primer coverage under More options; left blank, the paint's coverage is used.
This calculator includes 5 worked examples with independently sourced answers. They run in the test suite, and you can run them here too.