How Much Paint Do I Need?
Enter the room and get the gallons to buy. It deducts doors and windows, handles two coats, and adds up L-shaped rooms section by section.
Take this list to the store
We'll email the quantities above, what you typed in, and a link that reopens this calculator already filled in — so you can adjust it on your phone in the aisle.
How to work it out
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Measure the floor, not the walls
Length and width of the floor give you the perimeter, which is all the wall area calculation needs. It is faster than measuring four walls and less error-prone. L-shaped room? Add a section for each rectangle.
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Measure floor to ceiling
One measurement in a corner. If you are painting the ceiling too, switch that on — the ceiling area comes from the floor measurements you already entered.
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Count the openings
A standard door is roughly 21 sq ft, an average window about 12 sq ft. On one room this barely changes the answer; on a whole house it saves you several gallons.
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Decide on coats before you buy
Two coats is standard and is what the calculator assumes. One coat only works when you are refreshing the same color on a sound surface. Going dark over light, or painting bare drywall, plan on three — or prime first, which is cheaper than a third coat of color.
Gallons by room size
Walls only, 8 ft ceiling, one door and one window deducted, 350 sq ft per gallon.
| Room size | Wall area | One coat | Two coats | Gallons to buy |
|---|---|---|---|---|
| 8 × 10 ft | 255 sq ft | 0.7 gal | 1.5 gal | 2 |
| 10 × 10 ft | 287 sq ft | 0.8 gal | 1.6 gal | 2 |
| 10 × 12 ft | 319 sq ft | 0.9 gal | 1.8 gal | 2 |
| 12 × 12 ft | 351 sq ft | 1.0 gal | 2.0 gal | 3 |
| 12 × 14 ft | 383 sq ft | 1.1 gal | 2.2 gal | 3 |
| 12 × 16 ft | 415 sq ft | 1.2 gal | 2.4 gal | 3 |
| 14 × 16 ft | 447 sq ft | 1.3 gal | 2.6 gal | 3 |
| 16 × 20 ft | 543 sq ft | 1.6 gal | 3.1 gal | 4 |
“Gallons to buy” rounds two coats up to whole cans. Buying a quart to top up a part-gallon is usually cheaper.
What a gallon covers
| Surface | Coverage per gallon | Notes |
|---|---|---|
| Smooth, previously painted drywall | 350–400 sq ft | The best case. Most cans quote this figure. |
| New or primed drywall | 300–350 sq ft | Slightly thirstier on the first coat. |
| Textured (orange peel, knockdown) | 250–300 sq ft | Texture adds surface area you cannot see. |
| Bare wood or masonry | 200–250 sq ft | Prime it first or you will use far more. |
Tinted deep colors often cover less than the can claims. When in doubt take the lower figure.
How much paint for a 12x12 room?
A 12 × 12 ft room with an 8 ft ceiling has 384 sq ft of wall. Deduct one door and one window and you are painting about 351 sq ft. At 350 sq ft per gallon that is one gallon per coat, so two gallons for two coats.
Add the ceiling and you add 144 sq ft — another half gallon per coat.
Should you buy gallons or quarts?
A gallon costs far less than four quarts, so buy gallons for the bulk and a single quart only to top up. If the calculator says 2.3 gallons, buy two gallons and one quart rather than three gallons — you save money and you are not left with most of a can going off in the garage.
The exception is custom-tinted color. Getting an exact match on a second trip is not guaranteed, so for a tinted color buy the full amount in one go, from the same batch.
Do not forget primer
Primer is not paint and does not come out of this number. You need it when you are covering bare drywall, patches, stains, or going light over a dark color. One coat of primer covers about the same area as one coat of paint, so take the one-coat figure above.
Paint-and-primer-in-one products are paint with more solids. They help on a sound, similar-colored wall. They do not replace real primer on bare board.
Trim, doors and ceilings
- Trim and baseboard — roughly a quart per 100 linear feet, per coat.
- A door — about a quart covers both sides of two doors.
- Ceilings — use the ceiling toggle above; ceiling paint is flat and usually covers a little less.
How this is worked out
No black box — here is the arithmetic the calculator runs, so you can check it against your own numbers.
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perimeter = 2 × (length + width), summed over every sectionMeasuring the floor gives the same perimeter as measuring four walls, faster. -
wall area = perimeter × ceiling heightThe surface you are actually rolling. -
+ ceiling area = length × widthOnly when the ceiling is switched on. -
− (doors × 21) − (windows × 12)Average opening sizes in square feet. -
× number of coatsTwo is standard. Each coat is a full pass over the whole surface. -
÷ coverage per gallon350 sq ft is the realistic default; the can usually claims 350–400. -
whole gallons + quarts for the remainderA gallon costs far less than four quarts, so buy gallons and top up with one quart. -
remainder under 0.1 gal is droppedThat is about 35 sq ft — inside the margin of error on any coverage figure, and not worth a trip.
Common questions
How many square feet does a gallon of paint cover?
350 to 400 sq ft for one coat on smooth, previously painted drywall. Textured walls drop that to 250–300, and bare or porous surfaces to around 200. The figure on the can is a best case — take the lower end if you are unsure.
How much paint for a 10x10 room?
About 320 sq ft of wall at 8 ft ceilings, less around 33 sq ft for a door and window. That is roughly one gallon per coat, so two gallons for the usual two coats.
Do I really need two coats?
Almost always, yes. One coat leaves an uneven sheen and the old color showing through in patches under side light. The only safe single-coat job is refreshing the identical color on a wall in good condition.
How much paint for a whole house interior?
A rough rule for US homes is one gallon per 350 sq ft of floor area per coat for walls, plus a third again for ceilings. A 1,800 sq ft home is therefore in the region of 10–12 gallons for two coats on the walls. Measure room by room for anything you are actually buying.
Does dark paint need more coats?
Usually. Deep reds, blues and blacks carry more pigment and less hiding solid, so three coats over a light wall is common. A gray primer tinted towards the final color cuts it back to two, and costs less than an extra coat of expensive paint.
How do I work out an L-shaped room?
Press “Add another section” and enter each rectangle. The perimeter of each is worked out and added, so the wall area comes out right without you doing any arithmetic.
Should I deduct doors and windows?
For one room it makes little difference and leaves you a useful margin. For a whole house it is worth doing — twelve doors and twenty windows is close to 500 sq ft, or about a gallon and a half per coat.
How long should I leave between coats?
Follow the can, but four hours is typical for latex and overnight for oil-based. Recoating too early pulls the first coat off the wall and leaves visible drag marks.
Where these figures come from
Every figure below is traceable. How we check the numbers explains how they are verified, and the coverage reference collects them all in one place.
- Sherwin-Williams and Benjamin Moore technical data sheets — stated spread rate per gallon by product and sheen
- Paint Quality Institute guidance — coverage on textured, porous and previously painted surfaces
- Manufacturer application instructions — recoat times and when a primer coat is required
Think a number here is wrong? Tell us — we check every report, correct the page, and date the change. Last checked September 12, 2026.