How Much Paint Do I Need? Room-by-Room Guide

A gallon of paint covers about 350 square feet with one coat on a smooth wall. A typical 12 × 12 ft room with 8 ft ceilings has around 330 to 380 square feet of wall, so it takes just under 2 gallons for two coats. Here is how to work out the number for your own rooms, and the factors that move it up or down.

The formula

1. Wall area: add up the lengths of all walls (the perimeter) and multiply by the ceiling height. For a rectangular room, 2 × (length + width) × height.
2. Subtract openings: take off about 21 ft² for each standard door and 15 ft² for each typical window. Small windows are not worth deducting, because trim and touch-ups use that paint up.
3. Multiply by the coats you plan to apply (nearly always two).
4. Divide by the coverage of your paint (350 ft² per gallon unless the can says otherwise).

For a 12 × 12 ft room with 8 ft ceilings: walls are 2 × 24 × 8 = 384 ft². Take off one door and two windows (51 ft²) to get 333 ft². Two coats is 666 ft², and at 350 ft² per gallon that is 1.9 gallons, so buy 2 gallons.

Paint needed for common room sizes

These figures assume 8 ft ceilings, one door, two windows and two coats at 350 ft² per gallon.

The ceiling column is for two coats on the ceiling alone. A ceiling is usually painted in a flat finish, in a different paint from the walls, so it is bought separately.

What changes the coverage

• Surface texture. Rough or textured walls (orange peel, knockdown, brick, stucco) soak up much more paint, so assume 250 to 300 ft² per gallon.
• Bare or patched surfaces. New drywall, patches and unpainted wood absorb paint like a sponge. Prime them first, which is cheaper than extra coats of finish.
• Colour change. Going from dark to light, or covering a bold colour, can take three coats or a tinted primer. Deep, saturated colours often need more coats too.
• Paint quality. Better paint has more solids and covers more evenly, so it often needs fewer coats. A "paint and primer in one" can help on moderate changes.
• Application. Rollers use more than sprayers (which waste a lot of overspray, but are fast), and brushes on trim use little.

Don't forget the extras

• Trim and baseboards: a quart is typically enough for the trim in a single room.
• Doors: a standard door takes about a quart for two coats on both sides.
• Primer: if you need it, add its own coverage (about 300 to 400 ft² per gallon).
• Touch-ups: buy a bit more than you need and save the leftover, labelled with the room, colour and date.

Gallons, quarts and five-gallon buckets

Paint is sold in quarts, gallons and five-gallon pails. A quart covers about 87 ft². The calculator rounds your total up to the nearest quart, and gives it as gallons plus quarts. If your total is more than about four gallons, a five-gallon bucket is usually cheaper per gallon, and mixing everything in one bucket guarantees an even colour across the room.

Common questions

Do I really need two coats? Almost always. One coat rarely gives uniform coverage, and the color often looks patchy as it dries. The exception is going over a very similar colour with a good-quality paint.

Can I use the same paint on walls and ceiling? You can, but ceiling paint is formulated to splatter less, and flat finishes hide imperfections. For a big job it is worth buying it separately.

What if I have a lot of windows? Deduct them if they are large (such as sliding doors and big picture windows), and ignore small ones.