How Much Paint for a Room

How paint coverage works out

A gallon of wall paint covers about 350 square feet in one coat on a smooth, already painted surface. That figure comes from the manufacturer and assumes normal thickness, a good roller and no waste. Everything else moves the number down: bare drywall drinks the first coat, a textured wall has more surface than its footprint suggests, and a deep color going over a light one can need a third coat.

So the calculation is simple arithmetic with a few adjustments. Work out the paintable wall area, subtract the doors and windows, multiply by the number of coats, then divide by the coverage per gallon and round up. The calculator above does exactly that and shows every line, so you can see where the gallons come from rather than trusting a single number.

Two manufacturer charts are worth having open when you plan. Benjamin Moore's coverage guide and Sherwin-Williams' paint calculator both publish the same 350 square feet per gallon starting point with their own adjustment tables. If you are painting a home built before 1978, read the EPA's lead paint guidance before you sand or scrape anything.

Worked example: a 12 by 14 foot bedroom

A standard bedroom, 12 feet by 14 feet, with 8 foot ceilings, two doors and two windows. Two coats of paint.

• Wall perimeter: 2 × (12 + 14) = 52 linear feet
• Wall area: 52 × 8 = 416 square feet
• Subtract openings: 2 doors at 21 sq ft plus 2 windows at 15 sq ft = 72 square feet
• Paintable wall area: 416 − 72 = 344 square feet
• Two coats: 344 × 2 = 688 square feet
• Gallons: 688 ÷ 350 = 1.97, so buy 2 gallons

That is a clean result: two gallons, no leftover half can to store. Now add the ceiling at 12 × 14 = 168 square feet. One coat of ceiling paint brings the total to 688 + 168 = 856 square feet, which is 2.45 gallons, so you would buy 3 gallons and have about half a gallon spare for touch ups.

Cost it out at $35 a gallon for wall paint and $28 for ceiling paint: two gallons of wall paint is $70, one gallon of ceiling paint is $28, and you are at $98 in paint for the room. Add tape, a roller cover set and a tray, and a DIY bedroom repaint usually lands between $120 and $150 in materials.

Worked example: a living room with tall ceilings

Now a larger room where the numbers matter more. A living room 16 feet by 20 feet with 10 foot ceilings, three windows and two doors, painted in two coats.

• Perimeter: 2 × (16 + 20) = 72 linear feet
• Wall area: 72 × 10 = 720 square feet
• Subtract 3 windows and 2 doors: 45 + 42 = 87 square feet
• Paintable area: 720 − 87 = 633 square feet
• Two coats: 633 × 2 = 1,266 square feet
• Gallons: 1,266 ÷ 350 = 3.62, so buy 4 gallons

Now add a third coat on a 160 square foot accent wall, which is the case when a dark color is going back to a light one. That adds 160 square feet, taking the total to 1,426 and the answer to 4.08 gallons, so buy 5. In the calculator, set the coats field to 3 and it will show the larger number for the whole room, which is the safe way to buy.

At $40 a gallon that is $160 in paint, and a 5 gallon pail would bring it closer to $180. Tall ceilings also change the labor more than the paint: a 10 foot wall needs an extension pole and a step ladder, and cutting in at that height takes twice as long as at 8 feet.

One practical note on the extra coat. Dark to light is the direction that needs it. Light to dark usually covers in two coats, and if the new color is within a shade or two of the old one, one coat can sometimes work over a tinted primer. When in doubt, buy the third gallon and keep the receipt, because matching a batch later is harder than returning an unopened can.

Paint coverage and gallons by room size

The table below assumes 8 foot ceilings, two doors, two windows, and two coats. Use it as a sanity check on the calculator's answer rather than a replacement for it.

The cost column is wide because paint prices run from about $25 a gallon for a basic interior latex to $80 or more for a premium washable finish. If you are painting a hallway or a child's room where scrubbing is likely, the premium finish pays for itself, because you will not be repainting in two years.

Doors, windows, trim and the parts people forget

Wall area is the easy part. The rest of a repaint has its own math, and forgetting it is why a job stalls halfway through.

• Doors and windows. Subtract them from the wall area, but remember the casings around them still need paint. A door casing is roughly 18 linear feet, and there are two sides to every opening.
• Baseboard. A 12 by 14 room has about 52 linear feet of baseboard. At 6 inches tall that is 26 square feet, and a quart of trim enamel covers it twice over.
• Ceiling. Multiply length by width. A 12 by 14 ceiling is 168 square feet, and flat ceiling paint covers about the same 350 square feet per gallon.
• Closets. Easy to skip, and easy to notice later. Add the closet walls to the total if you are painting them.
• Primer. Count it as a full coat. A tinted primer on bare drywall does double duty as the first coat, which can save you a gallon of the finish paint.

Trim and doors are usually painted with a different product, often a waterborne alkyd or a semi-gloss enamel that cleans up better than flat wall paint. Buy a separate quart or gallon for them, and do not try to stretch wall paint onto the trim, because it will not hold up to the same wear.

Buying, storing and finishing the job

A few practical rules turn the estimate into a finished room without a second trip to the store.

Buy from one batch. The batch code is stamped on the can lid. Two cans from different batches can differ slightly in color, and on a long wall that difference is visible in raking light. If you need four gallons, ask for them from the same batch, or buy a 5 gallon pail.

Keep a little back. Pour about a cup into a small jar, label it with the room and the date, and store it somewhere that does not freeze. That jar is what saves you when a chair nicks the wall in a year. Paint keeps for several years when the lid is sealed properly.

Do not over-thin. Some people add water to make paint go further. It does, and it also thins the film, which shortens the life of the finish and makes the color less even. If coverage is the problem, buy the extra gallon instead.

Finally, plan the order. Ceiling first, then walls, then trim, then touch up. A roller spatters the trim if you do it the other way around, and cutting in the ceiling line is easier while the walls are still bare. Whatever the calculator returns, treat it as a materials estimate rather than a fixed quote, because surface condition and color choice can move the real number by a gallon or more.