Paint calculator guide

How Much Paint Do I Need for a Room?

Most bedrooms take 2 to 3 gallons for two coats on the walls, plus 1 gallon for the ceiling. Here is how to get the exact number for your room.

The formula

Wall area = 2 × (length + width) × height − 21 sq ft per door − 15 sq ft per window Gallons = wall area × coats ÷ coverage per gallon, rounded up

Do the same for the ceiling using length × width. Buy ceiling paint separately, since it is usually a different product from wall paint.

The label on the can gives the maker's coverage per gallon for one coat. These are typical ranges.

Surface	Sq ft per gallon	Notes
Smooth, previously painted drywall	350–400	The usual repaint
Textured walls or ceilings	250–300	Texture soaks up more paint
New drywall	Prime first	Primer seals the paper and mud so the topcoat covers evenly
Bare wood or masonry	200–300	Porous; check the product label

Assumes 8-foot ceilings, 1 door, 2 windows, 2 coats, and 350 sq ft per gallon.

Room size	Wall area	Wall paint	Ceiling paint
10' × 10'	269 sq ft	2 gal	1 gal
12' × 12'	333 sq ft	2 gal	1 gal
12' × 14'	365 sq ft	3 gal	1 gal
14' × 16'	429 sq ft	3 gal	2 gal
16' × 20'	525 sq ft	3 gal	2 gal

A 16' × 20' room lands at exactly 3.0 gallons. With any extra patching or a deep color change, buy a fourth.

Big color changes. Covering a dark color with a light one often takes primer or a third coat.
Higher ceilings. Recalculate with the real wall height. A 10-foot ceiling adds 25% more wall area than an 8-foot one.
Rough rollers and thick naps. They hold more paint and lay it on heavier.

Box your paint. When a job needs several gallons of one color, pour them together into a bucket and mix. It evens out small color differences between cans.
Price the 5-gallon bucket. When you need 4 or more gallons of one color, a 5-gallon bucket is often cheaper per gallon.
Keep a quart for touch-ups. Label it with the room, color name, and sheen.

Painting for a client? The estimator does this math for every room and prices the job.