How Much Paint Do I Need for a Room? (10×10, 12×12 and Up)

Quick answer: A 12×12 room with 8-foot ceilings needs about 1.5 to 2 gallons for two coats on the walls. A 10×10 room needs 1 to 1.5 gallons. Add roughly 1 gallon for the ceiling and 1 quart for the trim. Always buy 10 to 15 percent extra for touch-ups.

Running out of paint halfway through the second coat is the fastest way to ruin a weekend project. Buy too much and you have leftover gallons drying out in the garage. This guide gives you the exact amount for the most common room sizes, the formula behind it, and the adjustments that catch most people out. When you want the numbers done for you, our free painting calculator handles the math in seconds.

Paint needed by room size (at a glance)

The table below assumes 8-foot ceilings, two coats on the walls, and one standard door plus one window per room. Coverage is calculated at 350 square feet per gallon, the figure most interior paints print on the can.

Room size	Wall area (paintable)	Walls, 2 coats	+ Ceiling	Total to buy
10×10 ft	~284 sq ft	1.5 gal	+1 gal	2 to 2.5 gal
10×12 ft	~317 sq ft	2 gal	+1 gal	2.5 to 3 gal
12×12 ft	~349 sq ft	2 gal	+1 gal	2.5 to 3 gal
12×14 ft	~381 sq ft	2.5 gal	+1 gal	3 to 3.5 gal
14×16 ft	~445 sq ft	2.5 gal	+1.5 gal	3.5 to 4 gal
16×20 ft	~544 sq ft	3 gal	+1.5 gal	4 to 5 gal

These are buy-it figures, already rounded up to whole gallons and quarts because paint is sold that way. If you are painting walls only and keeping the ceiling white, drop the ceiling column.

The formula: how to calculate paint for any room

You do not need the table. The math is four short steps and works for any room shape.

Step 1: Measure the perimeter

Add the length of every wall you plan to paint. For a 12×12 room that is 12 + 12 + 12 + 12, which equals 48 feet.

Step 2: Multiply by ceiling height

Multiply the perimeter by the wall height. For a standard 8-foot ceiling: 48 x 8 = 384 square feet of gross wall area.

Step 3: Subtract doors and windows

A standard interior door is about 20 square feet. A standard window is about 15 square feet. For one of each, subtract 35 square feet: 384 – 35 = 349 square feet of paintable surface.

Step 4: Divide by coverage, then multiply by coats

Divide the paintable area by 350 (square feet per gallon): 349 / 350 = roughly 1 gallon per coat. For two coats, that is about 2 gallons. Round up to the nearest gallon when you shop.

That single example explains the entire table. Change the room dimensions and the same four steps give you the answer. Our paint coverage calculator runs this for you if you would rather plug in numbers than do arithmetic on the wall.

How much does a gallon of paint actually cover?

Most interior latex paints claim 350 to 400 square feet per gallon on a smooth, primed surface with a roller. Real-world coverage is usually closer to 350, and lower in three situations:

• Textured walls (orange peel, knockdown, popcorn): plan on 10 to 15 percent more paint. The texture has more surface area than a flat wall of the same dimensions.
• Spraying instead of rolling: a sprayer lays paint down faster but wastes more to overspray, dropping effective coverage to 150 to 250 square feet per gallon.
• Porous or bare surfaces: new drywall, fresh joint compound, and bare wood drink the first coat. Prime first so your finish paint covers as advertised.

Walls, ceiling and trim are three separate calculations

The most common buying mistake is treating a room as one number. Each surface uses a different product and a different quantity.

Walls

This is the perimeter-times-height calculation above. Wall paint is usually eggshell or satin in living spaces.

Ceiling

Ceiling area equals room length times width. A 12×12 room has a 144 square foot ceiling, so one gallon of flat ceiling paint covers two coats with room to spare. Larger rooms past 200 square feet of ceiling may need a second gallon.

Trim, doors and baseboards

Trim uses a small amount of semi-gloss or satin enamel. A quart covers the baseboards, door casings, and one or two doors in an average room. Buy a full gallon only if the room has heavy crown molding, wainscoting, or several doors.

How many coats will you really need?

The table assumes two coats, which is the honest default for almost every repaint. You can sometimes get away with one coat, and you will sometimes need three. Here is how to tell in advance.

Situation	Coats to plan for
Same color, freshening a clean wall	1 coat
New color, similar shade, primed wall	2 coats
Light over dark, or dark over light	2 coats + tinted primer
Bold reds, yellows and oranges	3 coats (these pigments cover poorly)
New drywall	1 primer + 2 finish coats

Always add a touch-up cushion

Buy 10 to 15 percent more than the calculation says. Walls are never perfectly smooth, rollers leave thin spots, and you will want matching paint for the inevitable scuff a year from now. A leftover quart from the exact batch is worth far more than a near-match mixed later, because dye lots drift between mixes.

Common mistakes that throw the number off

• Forgetting the second coat. One gallon covers a 12×12 room once. People buy one gallon, finish the first coat, and the hardware store is closed.
• Counting the ceiling in wall paint. Ceilings use flat white, not your wall color. Keep them separate.
• Ignoring vaulted ceilings. A cathedral ceiling adds wall height well past 8 feet. Measure to the peak, not the standard height.
• Underbuying for dark accent walls. Deep colors need more coats, so a single accent wall can use as much paint as two normal walls.

A full worked example: painting a master bedroom

Say you have a 14 by 16 foot master bedroom with 9-foot ceilings, two windows, one door, and a closet you are leaving alone. You want new wall color, a fresh white ceiling, and crisp trim. Here is the whole calculation.

Walls: perimeter is 14 + 16 + 14 + 16 = 60 feet. At 9 feet tall that is 540 square feet gross. Subtract two windows (30 square feet) and one door (20 square feet) to get 490 paintable square feet. Divide by 350 for one coat, multiply by two coats: 490 / 350 x 2 = 2.8 gallons. Buy 3 gallons.

Ceiling: 14 x 16 = 224 square feet. One gallon covers two coats at the 350 rate with margin, but because 224 is large, buy a second quart as insurance, or one gallon plus a quart.

Trim: baseboards, two window casings and one door casing in this room use about a quart of semi-gloss enamel for two coats.

Total shopping list: 3 gallons wall color, 1 gallon plus a quart ceiling white, 1 quart trim enamel. That single example shows how the three surfaces stack into a real cart.

Match the sheen to the room, not just the color

Sheen does not change how much paint you buy, but buying the wrong sheen for a room means repainting, which doubles your quantity for real. Use this as a quick guide:

Room or surface	Recommended sheen	Why
Bedrooms, living rooms	Eggshell or satin	Hides flaws, easy to wipe
Kitchens, bathrooms	Satin or semi-gloss	Handles moisture and scrubbing
Trim, doors, baseboards	Semi-gloss	Durable, takes knocks
Ceilings	Flat	Hides imperfections, no glare
Hallways, kids’ rooms	Satin	Most washable without shine

How paint quality changes the quantity

Cheap paint is a false economy when you are counting gallons. Budget paint has fewer solids and thinner pigment, so it covers less per coat and often needs a third coat to look even. A premium paint at 40 to 60 dollars a gallon genuinely covers more square footage and can turn a three-coat job into a two-coat job. When you compare prices, compare the cost to finish the room, not the price per can. A pricier paint that skips a coat is usually cheaper overall and less work.

Do not forget primer quantity

Primer is its own line on the shopping list. You need it on new drywall, on patched repairs, on bare wood, and whenever you make a big color jump such as white over deep navy. Primer uses the same coverage math as paint, roughly 300 to 400 square feet per gallon. For a single average bedroom, one gallon of primer covers any spots that need it. Tinting the primer toward your finish color improves coverage and can save you a finish coat, which is the cheapest way to cut your paint quantity.

Small spaces: closets, bathrooms and accent walls

Tiny rooms break the per-gallon intuition because they are mostly door, window and fixture. A small powder room or a reach-in closet usually fits inside a single quart to a single gallon for two coats, because once you subtract the door, mirror, vanity and window there is very little wall left. An accent wall is the opposite trap: a single deep-color wall can use as much as two normal walls because bold pigments need an extra coat to look solid. When in doubt on a small space, buy a gallon and expect leftovers rather than risk a second trip for a half-pint.

A simple supplies checklist

Once you know the gallons, round out the cart so you are not making a second trip:

• Paint and primer in the quantities above, plus the 10 to 15 percent cushion
• Roller covers (a 3/8 inch nap for smooth walls, 1/2 inch for light texture)
• Angled brush for cutting in edges and corners
• Painter’s tape and drop cloths
• Sandpaper and filler for prep
• A paint tray or a five-gallon bucket with a grid for larger rooms

How professional painters estimate paint

Pros rarely measure every wall on small jobs. They use a rule of thumb: roughly one gallon per 350 to 400 square feet of wall, two coats standard, and they add a fixed cushion per room. On bids they measure carefully because the paint is a real line item in the price. The difference between a homeowner and a pro is not the formula, it is the cushion and the experience to know which surfaces will drink an extra coat. That instinct is exactly what the painting calculator bakes in so you do not have to learn it the hard way.

From paint quantity to project cost

Knowing the gallons is half the budget. The other half is labor, prep and the paint grade you choose. If you are pricing a full interior project rather than a single room, our guide to interior painting cost breaks down the dollars per square foot, and the free painting estimate tool turns your measurements into a line-item quote you can hand a client or compare against a contractor’s bid.

Frequently asked questions

How much paint do I need for a 12×12 room?

About 1.5 to 2 gallons for two coats on the walls, plus roughly 1 gallon for the ceiling and a quart for trim. Buy 2.5 to 3 gallons total to cover walls and ceiling with a touch-up cushion.

Will one gallon paint a room?

One gallon covers a small 10×10 room for a single coat, or the walls of a closet or half-bath for two coats. For a normal bedroom with two coats, plan on two gallons.

How much paint for a 10×10 room with 8-foot ceilings?

Around 1.5 gallons for two coats on the walls. Add a gallon if you are also painting the ceiling.

Does primer count toward the total?

Primer is a separate product and a separate quantity. Budget one coat of primer on new drywall, bare wood, or when making a drastic color change, using the same coverage math as your finish paint.