Paint Calculator

How to calculate how much paint you need

Wall area = 2 × (length + width) × wall height. Subtract about 21 sq ft for each door (3 × 7 ft) and 15 sq ft for each window (3 × 5 ft). Multiply by the number of coats and divide by the coverage on the can, typically 350–400 sq ft per gallon. Add the ceiling (length × width) if you are painting it too.

Worked example: a 12 × 14 ft bedroom

With 8 ft walls the wall area is 2 × (12 + 14) × 8 = 416 sq ft. One door and one window leave 416 − 21 − 15 = 380 sq ft. Two coats make 760 sq ft, and at 350 sq ft per gallon that is 2.17 gallons — buy 2 gallons plus 1 quart.

How many coats do you need?

Two coats is the norm for an even finish, especially when changing color. One coat can be enough when repainting the same color in good condition. Going from a dark color to a light one, or painting new drywall, usually needs a coat of primer first.

Coverage and buying tips

Smooth, previously painted walls get close to the coverage on the label; textured, porous or patched surfaces use more. Buying 1 extra quart is cheaper than a second gallon, but if you would need 3 or more quarts, a gallon is usually the better buy — the calculator rounds this for you.

How much paint do I need for a 12 × 12 room?

With 8 ft walls, one door and one window, the walls are about 348 sq ft. Two coats at 350 sq ft per gallon need about 2 gallons.

How many square feet does a gallon of paint cover?

Most interior paints cover about 350–400 sq ft per gallon per coat on smooth walls. Check the label of your product and enter that figure.

How much paint do I need for a ceiling?

A 12 × 14 ft ceiling is 168 sq ft. Two coats at 350 sq ft per gallon need about 1 gallon.

Do I need to subtract doors and windows?

Yes for an accurate estimate. The calculator removes 21 sq ft per door and 15 sq ft per window; with very large windows or sliding doors, measure them and lower the count accordingly.