How the paint estimate works
Paint quantity comes down to two things: how much surface you are covering and how many times you are covering it. The calculator multiplies your wall area by the number of coats to get the total surface to be painted, divides that by how far a single can stretches, and rounds up to whole cans because you cannot buy part of one.
The default coverage of 350 square feet per gallon is a typical figure for one coat on a smooth, primed, mid-color wall. Rough, porous, or unprimed surfaces drink more paint and cover less, so lower the coverage figure when in doubt.
How many coats you really need
Two coats is the standard recommendation for a durable, even finish, and it is the default here for good reason — a single coat rarely hides the surface beneath it cleanly.
- Same or similar color over a clean wall: two coats is usually plenty.
- Dramatic color changes, especially light over dark or dark over light: budget a primer or tinted base coat plus two finish coats.
- Bold reds, yellows, and oranges: these pigments are thin and often need an extra coat to look solid.
- New drywall and bare wood: always prime first, then apply your finish coats.
Measuring the wall area
To find wall area, measure the length of each wall, add them together for the room perimeter, and multiply by the ceiling height. For a tighter estimate you can subtract large openings such as doors and picture windows, though leaving them in gives you a useful buffer for touch-ups.
Buy all your paint for one room at the same time and, ideally, from the same batch. Tints can vary subtly between mixes, and running short mid-job risks a visible seam where a new batch begins.
Caveats
This is a budgeting estimate. Actual coverage depends on the paint, the applicator, surface texture, and how heavily it is laid on. Spraying wastes more than rolling, and a heavily textured wall can cut coverage by a third or more. Always keep a little paint in reserve for repairs, and check the specific coverage printed on the can you choose.
Formula
totalArea = wallArea × coats; cans = ceil(totalArea / coveragePerCan)Frequently asked questions
- Should I subtract doors and windows?
- For a tighter estimate, subtract large openings from the wall area before entering it. Otherwise the small extra paint is a useful buffer.