Paint & interior finishes
How Much Paint Do I Need to Paint a Room?
By the HomeCalc USAReviewed against our editorial policyLast updated US units and pricing
Add the wall perimeter x ceiling height, subtract about 21 sq ft per door and 15 sq ft per window, divide by 350 sq ft per gallon, then multiply by the number of coats. A 12 x 14 ft room with 8 ft ceilings needs about 1.2 gallons per coat, so 2.5 gallons for two coats.
Skip the arithmetic: use the Paint Calculator.
Key takeaways
- 350 square feet per gallon per coat is the reliable planning figure for smooth interior drywall.
- Textured, porous or previously unpainted surfaces drop coverage to 250-300 square feet per gallon.
- Almost every job needs two coats; one coat only works when repainting a similar color with a quality paint.
- Prime bare drywall, patched areas, stains and any dramatic color change — primer is cheaper than a third coat of color.
Measuring the walls
Only subtract openings when they are large. Skipping small windows costs you a few square feet and gives a useful buffer against spills and roller waste.
- Add the length of all four walls to get the perimeter. A 12 x 14 ft room is 52 feet around.
- Multiply the perimeter by the ceiling height. 52 x 8 = 416 square feet of gross wall.
- Subtract 21 square feet for each standard door and about 15 square feet for each average window. One door and two windows: 416 - 51 = 365 square feet.
- Divide by 350 for gallons per coat: 365 / 350 = 1.04 gallons.
- Multiply by coats. Two coats = 2.1 gallons, so buy two gallons plus a quart, or round up to three for touch-ups.
Coverage rates by surface
| Surface | Sq ft per gallon, per coat |
|---|---|
| Smooth, previously painted drywall | 350-400 |
| Light orange-peel texture | 300-350 |
| Knockdown or heavy texture | 250-300 |
| New, primed drywall | 300-350 |
| Bare drywall without primer | 200-250 |
| Rough exterior stucco or masonry | 150-200 |
Ceilings and trim
Ceiling area is simply room length x width. A 12 x 14 ft ceiling is 168 square feet — under half a gallon per coat, but flat ceiling paint is thick and covers closer to 300 square feet per gallon, so budget a full gallon for two coats.
For trim, a rough rule is one quart per 100 linear feet per coat of baseboard, casing and crown. A standard door and its casing takes about a quarter of a quart per coat on both faces.
When you truly need two coats
- Any color change of more than a shade or two.
- Deep or saturated colors — reds, dark blues and yellows are the worst offenders and sometimes need three.
- Going from a dark color to a light one, which is far easier over a tinted primer.
- Flat or matte finishes, which telegraph roller lap marks after a single coat.
- New drywall, even after primer, because the paper and compound absorb differently.
Primer: when it pays for itself
Primer is not paint with a discount — it seals porous surfaces and blocks stains so the finish coat sits on top rather than soaking in. Use it on bare drywall, fresh joint compound, water or smoke stains, glossy surfaces after scuff sanding, and any bare wood or metal.
Tinting the primer to roughly your final color can eliminate an entire finish coat when covering a dark wall, which is usually the cheapest way to save both money and a day of work.
Buying and mixing
Buy all the paint for one room in a single trip and, if you need multiple gallons of a custom color, ask for them mixed together (boxed) in a five-gallon bucket. Tint batches vary slightly, and boxing prevents a visible shift halfway up a wall.
Leftover paint stored sealed and away from freezing keeps for two to three years and is worth having for touch-ups; write the room name and date on the lid.
Frequently asked questions
How many walls can a gallon of paint cover?
At about 350 sq ft per coat, one gallon covers roughly three to four walls of a 12 x 12 ft room with 8 ft ceilings (each wall is 96 sq ft) in a single coat. With the usual two coats, plan on about two gallons for that room.
How much paint do I need for a small bedroom or living room?
A small 10 x 10 ft bedroom with 8 ft ceilings has about 320 sq ft of wall before openings, so one gallon per coat, or two gallons for two coats. A 15 x 20 ft living room has about 560 sq ft, so roughly 3 to 4 gallons for two coats.
How many coats of paint do I need?
Two coats is the standard for walls. Plan on a primer coat as well over bare drywall, patched areas, or a large color change such as dark to light.
How much does 1 gallon of paint cover?
About 350 square feet in one coat on smooth, previously painted walls. Texture, porosity and application method push that down to 250-300.
How many gallons do I need for a 12x12 room?
With 8 ft ceilings, gross wall area is 384 square feet; after one door and one window, about 348. That is one gallon per coat, so two gallons for two coats, plus a gallon for the ceiling.
Do I need to subtract windows and doors?
Subtract them when a room has large openings or sliders. In an average bedroom, ignoring them simply builds in a sensible buffer.
Is one coat of paint ever enough?
Only when repainting the same or a very similar color with a quality paint over a sound, primed surface. Any real color change needs two.
Sources and references
- EPA — Lead-safe renovation rules for pre-1978 homes — Required practices when sanding or disturbing old paint.
- EPA — Volatile organic compounds and indoor air quality — Background for choosing low-VOC interior paint and ventilating during work.