How the paint estimate works

The calculator finds gross wall area from room perimeter and wall height, subtracts doors, windows, and any other excluded area, then applies the selected number of coats and waste allowance. Paint and primer are calculated separately because their coverage rates often differ.

Coverage and purchase assumptions

The default finish-paint coverage is 350 ft² per gallon per coat, and the default primer coverage is 300 ft². Actual spread rate changes with surface texture, porosity, application method, color change, and product. Enter the coverage printed on the selected can whenever possible.

A standard door is estimated at 21 ft² and a standard window at 15 ft². Use the other excluded-area field to correct for larger openings, built-ins, tile, or walls that will not be painted.

Gallons, quarts, and cost

The suggested purchase mix rounds required volume up to a whole quart and converts each group of four quarts to one gallon. The gallon-only result shows how many one-gallon cans cover the estimate. Cost uses the rounded gallon-and-quart equivalent at the entered per-gallon price; local quart pricing may be higher.

Worked example

A 12 × 10 ft room with 8 ft walls has 352 ft² of gross wall area. Subtracting one standard door and two standard windows leaves 301 ft². Two coats, 10% waste, and 350 ft² per gallon require about 1.89 gallons, which rounds to a suggested purchase of 2 gallons.

Planning notes

• Measure each room or wall section and add separate estimates when heights differ.
• Do not subtract openings when the trim, doors, or windows will receive the same product.
• New drywall, repairs, stains, and major color changes may need primer or extra coats.
• Confirm product coverage, container sizes, tint availability, and return policy before buying.

Paint calculator FAQ