Coverage per gallon by surface
The 350 figure comes off the data sheet. Sherwin-Williams specifies SuperPaint interior latex at 350 to 400 square feet per gallon applied at 4 mils wet, and that assumes a smooth, sealed, previously painted wall. Every other surface covers less, because the paint is filling texture or soaking into a porous substrate rather than sitting on top.
The calculator uses 350 for walls, 300 for primer and treats doors and trim as a separate product. The litre column is the same figure for a Canadian 3.79 L can, which is exactly a US gallon.
| Surface | Sq ft per gallon | Per litre | Why |
|---|---|---|---|
| Smooth, sealed, previously painted wall | 350–400 | 8.6–9.8 m² | the data sheet figure at 4 mils wet |
| Textured, knockdown or popcorn | 280–320 | 6.9–7.9 m² | texture hides 10–20% more surface |
| New drywall, PVA primer first | 250–400 | 6.1–9.8 m² | board and compound drink at different rates |
| Rough or freshly patched plaster | 250–300 | 6.1–7.4 m² | porous, soaks the first coat |
| Bare concrete block, block filler | 75–125 | 1.8–3.1 m² | filler, before any finish coat |
| Masonry finish coat over filler | 200–250 | 4.9–6.1 m² | still rougher than drywall |
| Door and trim enamel (Advance) | 400–500 | 9.8–12.3 m² | waterborne alkyd, thinner film |
| Door and trim enamel (ProClassic) | 350–400 | 8.6–9.8 m² | the acrylic alternative |
Spraying breaks these numbers. Airless transfer efficiency is commonly quoted at 40 to 70 percent, so a real share of every gallon lands as overspray. Add material if you spray, and mask properly.
Gallons by wall area
Divide the wall area by 350 for one coat and double it for two, then round up to whole cans. Two coats of 500 square feet is 2.86 gallons, so three cans. The exact figure is worth keeping because a room that lands at 2.06 needs a third gallon and one at 1.94 doesn’t.
Two coats is the default for almost any colour change and for any flat or matte finish. One coat is only honest when you’re repainting the same colour in the same sheen over sound paint.
| Wall area | 1 coat | 2 coats | Cans to buy, 2 coats |
|---|---|---|---|
| 100 sq ft | 0.29 gal | 0.57 gal | 1 |
| 200 sq ft | 0.57 gal | 1.14 gal | 2 |
| 300 sq ft | 0.86 gal | 1.71 gal | 2 |
| 400 sq ft | 1.14 gal | 2.29 gal | 3 |
| 500 sq ft | 1.43 gal | 2.86 gal | 3 |
| 600 sq ft | 1.71 gal | 3.43 gal | 4 |
| 800 sq ft | 2.29 gal | 4.57 gal | 5 |
| 1,000 sq ft | 2.86 gal | 5.71 gal | 6 |
| 1,500 sq ft | 4.29 gal | 8.57 gal | 9 |
| 2,000 sq ft | 5.71 gal | 11.43 gal | 12 |
A 5 gallon bucket covers 1,750 square feet in one coat or 875 in two, which is the walls of about three average bedrooms.
How many gallons for a 12 by 12 room
Two gallons for two coats on the walls. A 12 by 12 room has a 48 ft perimeter, so at 8 ft that’s 384 square feet of wall, or 324 once three openings come off at the 20 square feet each the calculator uses. Two coats is 648 square feet, which is 1.85 gallons. Buy two.
Ceiling height moves it. At 9 ft the same room is 2.13 gallons and needs three cans, and at 10 ft it’s 2.40. The 144 square foot ceiling takes well under a gallon of flat in two coats, and that’s a separate can because ceiling paint is a different product.
A 10 by 10 room is 1.49 gallons at 8 ft and still fits in two cans at 9 ft. A 12 by 16 is 2.22 and needs three. The paint calculator page has the full room-size table with the 8, 9 and 10 ft columns.
Litres, square metres and the Canadian can
A US gallon is 3.785 litres and 350 square feet is 32.5 square metres, so interior paint covers about 8.6 square metres per litre on smooth walls. The 37 m² or 400 square feet printed on a Canadian label is the manufacturer’s smooth-surface figure, and the working number is the lower end of the range.
A 4 litre can is near enough a gallon that every figure on this page applies. A 1 litre can covers about 8.6 square metres per coat, or 4.3 in two coats, which is one standard interior door with its frame.
Two worked examples
A painter has a circular entry 14 feet across to paint, and a gallon of the floor paint covers 250 square feet. Is one gallon enough? The radius is 7 ft, so the area is 3.1416 × 7 × 7, which is 153.9 square feet. That’s well inside 250, so yes, one gallon covers it in a single coat, with about 96 square feet to spare. A second coat would need 308 square feet and a second gallon.
Tony paints 500 square feet of wall with 2 gallons. How much paint is that per square foot? Two gallons divided by 500 square feet is 0.004 gallons per square foot, or the other way round, 250 square feet per gallon. That’s a plausible real-world figure for a first coat on a wall that drinks a little, and below the 350 a data sheet promises.
What eats the extra paint
Deep colours over light walls almost always need two coats and a tinted primer, whatever the can says. New drywall takes a PVA primer first at 250 to 400 square feet per gallon, and masonry needs a block filler before paint at 75 to 125. Roller nap matters too. A 3/4 inch nap on a smooth wall leaves a heavy film and burns through paint about 20 percent faster than a 3/8 inch nap.
Keep the leftovers. Box all the cans of one colour together before you start so the last wall matches the first, and a part gallon in the garage is the touch-up kit for the next three years.
Sources
The 350 to 400 figure is from the Sherwin-Williams SuperPaint interior data sheet. Door enamel coverage is from the Benjamin Moore Advance and Sherwin-Williams ProClassic product pages. The surface adjustments are the paint calculator’s own.
Sherwin-Williams SuperPaint Interior product page ↗SuperPaint Interior Flat product data sheet (PDF) ↗Benjamin Moore Advance Interior Paint ↗IRC R311.2 egress door (UpCodes) ↗
Run your numbers
Room length, width, wall height, openings and coats in, gallons and whole cans out, with ceiling, primer and doors on separate lines. Then the drywall calculator if the walls aren’t up yet.
Common questions
How much does a gallon of paint cover?
About 350 to 400 square feet in one coat on a smooth, sealed, previously painted wall. On textured, patched or bare surfaces figure 250 to 300. Two coats halves whichever figure you use.
How much does a gallon of paint cover with 2 coats?
About 175 square feet of wall, from the 350 square feet a gallon covers in one coat. A 12 by 12 room with an 8 ft ceiling is 324 square feet of wall after openings, so two coats takes two gallons.
How many gallons of paint do I need for a 12x12 room?
Two gallons for two coats on the walls at an 8 ft ceiling, three at 9 or 10 ft. Ceiling paint is a separate can and the 144 square foot ceiling stays under a gallon for two coats.
How far will a gallon of paint go?
One coat on the walls of a 10 by 10 room with an 8 ft ceiling, or two coats on a 5 by 8 bathroom. In square feet, about 350 in one coat.
How much does a quart of paint cover?
About 87 square feet in one coat. That’s one interior door in two coats, both faces and all edges, with a little to spare. It won’t do the door and its frame.
How much does a 5 gallon bucket of paint cover?
About 1,750 square feet in one coat or 875 in two. That’s the walls of three or four average bedrooms, and it costs less per gallon than five singles.
How many square metres does a litre of paint cover?
About 8.6 square metres per coat on smooth walls, from 350 square feet per US gallon. A 3.79 L Canadian can is a US gallon, so it covers about 32 square metres per coat.
A painter must paint a circular entry 14 feet in diameter. A gallon covers 250 square feet. Is one gallon enough?
Yes. The area is π × 7² = 153.9 square feet, which is less than 250, so one gallon covers it in one coat with about 96 square feet to spare.