Free calculator
Paint calculator: how much paint do I need?
A gallon of paint covers about 350 to 400 square feet per coat, so two coats on the 338 sq ft of wall in a 12 x 12 ft room take 1.93 gallons: buy 2. Enter the room or the wall area, the number of coats and the coverage printed on the can, and get how much paint to buy.
Result
- Wall area (gross)
- 45 m²
- Paintable area (net)
- 41.9 m²
- Paint needed (2 coats)
- 8.38 L
- Cans to buy (5 L)
- 2
- Total bought
- 10 L
Walls only. Add the ceiling area separately if you paint it, and a primer coat on new plaster.
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How it works
Wall area of a room is the perimeter times the height: 2 × (length + width) × height. Doors and windows are deducted at typical sizes (about 1.9 m² or 20 sq ft per door, 1.2 m² or 13 sq ft per window). Paint needed = net area × coats ÷ coverage.
Coverage is the figure the manufacturer prints on the can. Sherwin-Williams (2026) puts a gallon at about 350 to 400 sq ft per coat, which is 8.6 to 9.8 m² per litre; many metric cans print 10 m² per litre, the figure the calculator starts at. Bare plaster, textured or dark walls absorb more, so use the lower end of the range or add a coat.
Switched to US units, the calculator shows that starting figure as 407 sq ft per gallon. The guides on this site plan with 350, the low end of the range: type 350 in the coverage box and you get exactly the figures in the 12x12 room guide, the ceiling paint guide and the whole-house guide.
The calculator covers walls only. Add the ceiling area separately if you paint it, and count a primer or mist coat on new plaster as an extra coat.
Paint coverage: what 1, 2 and 5 gallons cover
Coverage per gallon divided by the coats. At the low end of the range, 350 sq ft per gallon is 0.0029 gallons per square foot per coat; the gallon coverage guide breaks it down by surface.
| Paint | 1 coat (350) | 1 coat (400) | 2 coats (350) | 2 coats (400) |
|---|---|---|---|---|
| 1 gallon | 350 sq ft | 400 sq ft | 175 sq ft | 200 sq ft |
| 2 gallons | 700 sq ft | 800 sq ft | 350 sq ft | 400 sq ft |
| 5 gallons | 1,750 sq ft | 2,000 sq ft | 875 sq ft | 1,000 sq ft |
Gallons for common wall areas
The other way round: the square feet of wall you measured, divided by 350, times the coats, rounded up to whole gallons.
| Wall area | 1 coat (gal) | Buy | 2 coats (gal) | Buy |
|---|---|---|---|---|
| 100 sq ft | 0.29 | 1 gal | 0.57 | 1 gal |
| 200 sq ft | 0.57 | 1 gal | 1.14 | 2 gal |
| 300 sq ft | 0.86 | 1 gal | 1.71 | 2 gal |
| 400 sq ft | 1.14 | 2 gal | 2.29 | 3 gal |
| 500 sq ft | 1.43 | 2 gal | 2.86 | 3 gal |
| 750 sq ft | 2.14 | 3 gal | 4.29 | 5 gal |
| 1,000 sq ft | 2.86 | 3 gal | 5.71 | 6 gal |
Frequently asked questions
- How much paint do I need for a 12 x 12 ft room?
- With 8 ft walls that is 384 sq ft gross. Taking out one door and two windows leaves about 338 sq ft; two coats at 350 sq ft per gallon is 1.93 gallons, so 2 gallon cans. The 12 x 12 ft ceiling adds 0.82 gallons for two coats.
- How many square feet does 2 gallons of paint cover?
- About 700 to 800 sq ft with one coat at 350 to 400 sq ft per gallon, or 350 to 400 sq ft with two coats: enough for the walls of a 12 x 12 ft bedroom at two coats. Five gallons cover 1,750 to 2,000 sq ft once.
- How many gallons of paint per square foot?
- About 0.0029 gallons per square foot per coat at 350 sq ft per gallon (0.0025 at 400). In practice: 0.29 gallons for 100 sq ft with one coat and 0.57 with two, so a gallon can either way.
- How much does a litre of paint cover?
- About 10 m² (108 sq ft) per coat at the 10 m² per litre printed on many metric cans, the calculator's starting value. US cans at 350 to 400 sq ft per gallon work out at 8.6 to 9.8 m² per litre.
- How many coats of paint do I need?
- Two coats is the usual assumption for a colour change on a painted wall. Covering a dark colour with a light one, or painting new plaster, often takes three including the primer.
- How much does a gallon of primer cover?
- Less than paint: Sherwin-Williams gives about 200 to 300 sq ft per gallon. Count the primer as its own coat at the coverage printed on the primer can.
- Is one litre of paint enough for one wall?
- At 10 m² per litre, one litre covers a 4 × 2.5 m wall once. Two coats need two litres, so a 2.5 L can is the practical minimum.
Guides
- How much paint do I need for a 12x12 room?
A 12x12 room with 8 ft ceilings has about 338 sq ft of wall: 1.93 gallons for two coats at 350 sq ft per gallon, so buy 2. Litres, 9 and 10 ft, ceiling.
- How many square feet does a gallon of paint cover?
A gallon covers about 350 to 400 sq ft on smooth walls, less on rough or bare surfaces. Gallons for 400 to 2,000 sq ft at one and two coats, and litres per square metre.
- How much paint do I need for a ceiling? Ceiling paint calculator for 10x10 to 20x20 ft
A 12x12 ceiling is 144 sq ft: 0.82 gallons for two coats at 350 sq ft per gallon, so 1 gallon or 4 quarts. 10x10 to 20x20, textured, and litres.
- How much paint for a 10x10 room? (10x12, 12x14 and 14x16 too)
Gallons of paint for a 10x10 room with an 8 ft ceiling, a door and two windows, one or two coats, plus the ceiling; 10x12 to 14x16 rooms; 3x3 to 4x5 m rooms in litres.
- How many square feet does a quart of paint cover?
A quart covers about 90 to 100 sq ft with one coat: what that means for a door, a wall, trim and a small ceiling at one and two coats, plus litres and 5 gallon pails.
- How much stain do I need for a fence? 50 to 300 ft
Gallons of stain or paint for a 6 ft wood fence from 50 to 300 ft, one or both sides, at one and two coats on rough or smooth boards, plus litres for metric fence panels.
- How much exterior paint do I need for a house? (1,000 to 3,000 sq ft)
Gallons of exterior paint for one and two storey houses of 30x40 to 40x60 ft at one and two coats on smooth and rough siding, openings deducted, trim, and litres.
- How much driveway sealer do I need?
5 gallon pails of asphalt sealer for 10x20 to 24x40 ft driveways at one and two coats on smooth and rough blacktop, from the coverage printed on the pail, and metric.
- How much paint for a whole house interior? (1,000 to 3,000 sq ft)
Gallons of wall paint for 1,000 to 3,000 sq ft homes with 8 and 9 ft ceilings at two coats, ceilings and trim counted separately, from a 12x12 room ratio, plus litres.