How many gallons of paint for a 12x12 room?

2 gallons for two coats on the walls of a 12 ft × 12 ft room with 8 ft ceilings, one door and two windows — the math is 333 ft² × 2 coats ÷ 350 ft²/gal = 1.90, rounded up. One coat only needs 0.95 gallons, which still rounds up to 1 because you cannot buy a fraction of a can. Add the ceiling and two coats climbs to 2.73 gallons, still 3 to buy.

How much does a gallon of paint cover?

About 350 square feet per coat on smooth, primed drywall — the figure this calculator defaults to. The real range runs from 250 to 400 ft² per gallon: heavily textured walls, bare wood and unprimed drywall sit toward the bottom, and smooth previously-painted walls sit toward the top. Check the can's label for the manufacturer's number on your specific paint before you rely on the default.

How many coats of paint do I need?

Two, in almost every case — one coat rarely hides brush marks, roller lines or the color underneath evenly. A single coat can work when you are repainting the exact same color, and a third coat is common when you are covering a dark wall with a light color or painting bare drywall, both of which soak up more of the first coat than they show.

Do I subtract doors and windows?

Yes. A standard interior door removes about 21 square feet of wall and a typical window about 15 square feet — both are subtracted from the wall area before the coats and coverage math runs. Skipping this step on a room with several openings is the single most common reason a paint estimate comes out too high.

How much paint for one wall?

A single 12 ft wide, 8 ft high wall is 96 square feet. At two coats and 350 ft²/gal that is only 0.55 gallons — under a full can, so buy quarts instead: 3 quarts covers it, since a gallon holds 4 quarts. Buying a full gallon for one accent wall usually leaves most of the can unused.

How much paint to cover a ceiling?

A ceiling is length × width, the same rectangle as the floor. A 12 ft × 12 ft ceiling is 144 square feet, and at two coats and 350 ft²/gal that needs 0.82 gallons — buy 1. Ceiling paint is usually a flat finish bought separately from the wall color, so tally it as its own line rather than folding it into the wall total.

How much paint for the interior of a house?

Add up the wall area room by room. Two 12×12 bedrooms, a 16×20 living room and a 10×12 kitchen, all with 8 ft walls, come to 1,696 square feet of wall before subtracting any doors or windows. Two coats at 350 ft²/gal needs 9.69 gallons — call it 10 — at roughly $350 in paint alone. Run each room through the calculator above and subtract its own doors and windows for a tighter number.

Construction

Paint Calculator

Paint needed is wall area minus doors and windows, times coats, divided by coverage per gallon. Enter a room by dimensions or type in the wall area directly, add the ceiling if you're painting it, and get gallons, quarts and liters to buy, plus cost.

Room

Enter length, width and wall height — the perimeter and wall area are worked out for you.

Length

Width

Wall height

Also paint the ceiling

Doors & windows

Doors

Windows

Area per door

ft²

Area per window

ft²

Paint

Coats

Coverage250–400 ft²/gal is typical

ft²/gal

Price per gallon

$/ gal

Paint to buy

2 × (12.0 + 12.0) × 8.0

Exact

1.903 gal

Paintable area

333 ft²

384 ft² of wall, minus 51 ft² of doors and windows.

Estimated cost

$70

2 gal @ $35.00

Try a room

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1 gallon = 4 quarts = 3.785 liters. A standard door is 21 ft², a typical window 15 ft².

The basics

How much paint a room needs

Every paint estimate is the same three moves: find the area you are actually painting, multiply it by how many coats it gets, then divide by how far one gallon stretches. The part people skip is subtracting the doors and windows — a rectangle of wall that never gets a drop of paint.

paintable = wall − openings

Wall area, minus what you don't paint

Wall area is perimeter times height. A door and a window are rectangles of drywall you never paint, so their area is subtracted before anything else happens. A ceiling, if you’re doing it, is added back on top — it has no openings of its own to net against.

384 ft² − 51 ft² = 333 ft²

gallons = area × coats ÷ coverage

Then scaled by coats and coverage

Each coat repaints the whole area again, not a fraction of it, so coats multiply the total. Coverage — how far one gallon spreads — divides it back down. The result always rounds up, because a can is a can.

333 ft² × 2 ÷ 350 = 1.90 gal → buy 2

Method

How to size a paint job by hand

Four steps take you from a tape measure to a number you can read off a paint-store shelf.

1
Find the wall area
Multiply the room’s perimeter by the wall height. Perimeter is 2 × (L + W) for a rectangular room — measure the floor, not the walls, since the perimeter is the same at every height.
2 × (12 + 12) × 8 = 384 ft²
2
Subtract doors and windows
Take off roughly 21 ft² per standard door and 15 ft² per window. Measure your actual openings if they run larger or smaller than average — a patio slider or a picture window is worth measuring exactly.
384 − 51 = 333 ft²
3
Add the ceiling if you're painting it
A ceiling is length × width, the same rectangle as the floor. Add it to the paintable area rather than netting it against the wall openings — it has no doors or windows of its own.
333 + 144 = 477 ft²
4
Multiply by coats, divide by coverage, round up
Gallons equal paintable area times coats, divided by coverage per gallon — 350 ft² is the usual middle figure. Round the answer up to a whole can; under a gallon, round up to the nearest quart instead.
333 × 2 ÷ 350 = 1.90 → buy 2 gal

Worked examples

The same 12×12 room, three ways

One bedroom — 12 ft × 12 ft, 8 ft walls, one door, two windows — carried through one coat, two coats, and two coats with the ceiling included. Every figure below is computed by the same logic as the calculator above.

1 coat, walls only

1 gal

333 ft² × 1 ÷ 350 = 0.95 gal, rounded up.

2 coats, walls only

2 gal

333 ft² × 2 ÷ 350 = 1.90 gal, rounded up.

2 coats, plus ceiling

3 gal

477 ft² × 2 ÷ 350 = 2.73 gal, rounded up.

Where it shows up

Why this math matters

one room at a time

Repainting a bedroom or living room

The most common use: a color change on one room, where getting the can count right means one trip to the store instead of two, and no leftover gallon of a color you’ll never use again.

room by room, then add

Repainting a whole house

A whole-house repaint is just this calculation run once per room and summed. Doing it room by room, rather than guessing from total square footage, is what keeps a five-room job from running a can or two short.

bare wood covers less

Exterior siding and trim

The same formula works outside, but bare or weathered wood siding covers far less than interior drywall per gallon — check the reference table below before you order paint for an exterior job.

Reference

Paint coverage by surface

The 350 ft²/gal default assumes smooth, previously-painted drywall. Every other surface covers differently, and using the wrong figure is the most common reason a paint order comes up short.

Surface	Coverage	Note
Smooth drywall or plaster	350–400 ft²/gal	The finish coat this page's 350 default assumes
Lightly textured drywall	300–350 ft²/gal	Orange-peel or light knockdown texture
Heavily textured or stucco	200–250 ft²/gal	Popcorn ceilings, heavy stucco, rough render
New bare drywall (unprimed)	200–300 ft²/gal	The paper face soaks up the first coat
Primed wood or trim	350–400 ft²/gal	Smooth, sealed surfaces paint efficiently
Bare wood siding	250–300 ft²/gal	End grain and rough boards drink more paint
Brick or block, unpainted	100–200 ft²/gal	Porous masonry is the thirstiest surface here
Metal, primed	350–400 ft²/gal	Doors, railings, ductwork

Sheen guide

Which finish for which room

Coverage doesn’t change much by sheen, but durability and where it belongs in a house does. Higher gloss resists scrubbing better and shows more of what’s underneath it.

Sheen	Durability	Best for
Flat / matte	Lowest — best at hiding surface flaws	Ceilings, low-traffic bedrooms
Eggshell	Light, wipeable	Living and dining rooms, hallways
Satin	Good, wipeable	Kids' rooms, family rooms, most walls
Semi-gloss	High, scrubbable	Kitchens, bathrooms, trim and doors
Gloss	Highest, fully washable	Cabinetry, doors, high-touch trim

Worth knowing

Rules worth remembering

Six facts that turn a paint order from a guess into a decision.

1 gal = 4 qt = 128 fl oz

A gallon breaks into quarts

For a single wall or a small touch-up, buying by the quart avoids paying for most of a can you’ll never open again. Four quarts always make one gallon exactly.

0.55 gal for one wall → buy 3 qt

1 gal = 3.785 L

Converting to liters is a straight multiply

Paint sold by the liter overseas uses the same formula throughout — just convert the coverage figure and the answer along with it. The calculator above does this for you with the unit picker on the result.

2 gal = 7.6 L

coverage 250–400 ft²/gal

Coverage is a range, not a constant

The number printed on a can is measured on a smooth, primed surface in ideal conditions. Texture, porosity and even the paint’s own quality tier move it — check the label rather than trusting one default figure for every job.

dark to light needs a coat more

Color change can force a third coat

Going from a dark wall to a light color, or the reverse, is the classic case where the default two coats undercounts. Budget a third coat whenever the contrast between old and new color is large.

2 coats is the default for a reason

Coats multiply the whole area

A second coat is not a flat top-up — it repaints everything the first coat touched. Underestimating this is why “one more coat” quietly doubles a paint order that already seemed generous.

primer seals bare drywall

New drywall drinks the first coat

Unprimed drywall and patched spots absorb finish paint unevenly, which can force an extra finish coat just to even out the sheen. A cheaper coat of primer usually avoids that.

Quick chart

Paint for common room sizes

The answer to “how many gallons of paint for a 14×14 room” and every size around it — square rooms at the two standard wall heights, two coats, walls only, no openings subtracted yet. Subtract your own doors and windows above for an exact number.

Gallons of paint needed for square rooms of common sizes
Room size	8 ft walls	9 ft walls
10 × 10 ft	2 gal	3 gal
12 × 12 ft	3 gal	3 gal
14 × 14 ft	3 gal	3 gal
16 × 16 ft	3 gal	4 gal
18 × 18 ft	4 gal	4 gal
20 × 20 ft	4 gal	5 gal

Two coats, 350 ft²/gal coverage, walls only. Doors, windows and any ceiling are not subtracted here — use the calculator above for those.

Common mistakes

Where paint estimates go wrong

Six errors account for almost every short order and every half-used leftover can.

walls, not floor

Using floor area instead of wall area

A room's floor area and its wall area are unrelated numbers. Paint covers the walls, so the estimate always starts from perimeter times height, never from the length times width of the floor.

subtract the openings

Forgetting doors and windows

A door removes a sizeable rectangle of wall and a window a smaller one. Skipping that subtraction on a room with several openings routinely overstates the paint needed by half a can or more.

coats multiply the area

Treating a second coat as a flat extra

A second coat does not add a fixed amount of paint — it needs the whole paintable area again. Doubling the coat count doubles the paint, whatever the size of the room.

350 is a middle figure

Assuming every surface covers the same

Coverage swings from around a hundred square feet a gallon on bare masonry to four hundred on smooth primed drywall. Using the label figure for the wrong surface is the most common source of a short order.

round up, always

Buying the exact calculated amount

Paint is sold by the can, not the fraction of a can, and mixing a fresh batch mid-wall risks a visible seam or a slightly different tint. Round up to the next gallon or quart rather than cutting it exact.

primer earns its cost back

Skipping primer on bare or patched drywall

Unprimed drywall and patched spots absorb paint unevenly, which can mean an extra coat of finish paint just to hide the blotching. One coat of primer is usually cheaper than the finish coat it saves.

FAQ

Common questions

Start from the walls, not the floor: a 12 ft × 12 ft room has a perimeter of 2 × (12 + 12) = 48 ft, so 8 ft walls give 384 square feet of wall. Subtract a standard door and two windows (51 ft²) and you are painting 333 square feet. At two coats and the usual 350 ft² a gallon, that is 1.90 gallons — buy 2.

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