Paint Calculator

Room length, width and ceiling height

Measure the room with a tape measure. A laser measure works too.

1. Length and width: measure wall to wall along the floor, to the nearest half foot. Length and width are interchangeable.
2. Ceiling height: measure from the floor to the ceiling. Standard ceilings are often 8 feet, but many newer homes have 9 or 10.
3. Not a simple rectangle? Split the room into rectangles, run the calculator for each, and add the gallons.
4. Walls are rarely perfectly straight, so measure in a couple of places and use the larger number.

The tool assumes a flat ceiling. For a vaulted or sloped ceiling, use the highest height for a safe estimate.

Doors and windows

These are subtracted because you will not be painting them.

1. Count the doors and windows in the room.
2. The tool takes off 20 square feet per door (a 3 by 7 foot door) and 15 square feet per window (3 by 5 feet).
3. For a large window, a sliding glass door or a wide opening, count it as two. If you are painting the trim, or want a bit more paint to be safe, enter fewer.

Coats

The number of coats of paint you plan to apply.

1. Two coats is a good plan for most rooms.
2. Use two or more when going over a dark color, changing color a lot, or painting new drywall. New or patched drywall usually needs primer first, which also takes paint.
3. One coat can work when the new color is close to the old one and you use a paint that hides well. The can usually says so.

Coverage (sq ft per gallon)

How much wall area one gallon covers with a single coat.

1. Read the label on the paint can, or the product page. It says something like "covers up to 400 sq ft per gallon".
2. Use a lower number than the maximum. Rough, textured or very porous surfaces soak up more paint.
3. If you have not chosen a paint, 350 square feet per gallon is a reasonable planning number.