How do I work out wall area for paint?

Add the length of every wall, multiply by the height, and take off doors and windows.

How many coats of paint do I need?

The label for your product says. A big color change or a porous wall may need more than the label minimum.

Should I buy extra paint?

Round up to whole cans, and keep what is left for touch-ups. Buying it all at once keeps the tint consistent.

HyreRemodel tools

Paint coverage calculator

Enter the wall perimeter and height, the openings, the number of coats, and the coverage printed on your paint.

A paint coverage calculator divides the wall area times the number of coats by the coverage per gallon on the label. A 12 × 12 ft room with 8 ft walls, less 40 sq ft of openings, is 344 sq ft. Two coats at 400 sq ft per gallon is 1.7 gallons: buy 2.

Work out your paint

Arithmetic on your figures. Nothing is stored or emailed.

— Paint needed

— To buy

— Area per coat

What this assumed —

A quantity, not a quote. Primer is a separate calculation.

Worked example

A 12 × 12 ft room, two coats

Wall area

48 ft of wall × 8 ft high = 384 sq ft. Take off 40 sq ft for a door and two windows: 344 sq ft per coat.

Gallons

Two coats is 688 sq ft. At 400 sq ft per gallon, that is 1.7 gallons, so buy 2. At 450, it is 1.5.

Gallons = (perimeter × height − openings) × coats ÷ coverage per gallon.

Where the coverage figure comes from

Paint coverage is printed by the maker for each product. Benjamin Moore lists Benjamin Moore Regal Select interior, satin/pearl at 400–450 sq ft per gallon on its product page. The calculator starts at 400, the low end.

Your product’s figure replaces it. Read the label or the technical data sheet for the paint you buy. Coverage is a figure for a smooth, primed surface.

Rough, porous or patched walls take more. So does a big color change. New drywall usually needs a primer first; see the drywall calculator if you are hanging it.

Painting in a home built before 1978

Sanding or scraping old paint can release lead dust. Paid work disturbing more than 6 sq ft per room inside, or 20 sq ft outside, needs an EPA Lead-Safe Certified firm.

Test before you sand. Homeowners working on their own home are generally outside the rule, but the dust is just as hazardous.

What the paint calculator leaves out

The paint calculator gives no price. Multiply the cans by the price on the shelf or the bid. For cabinets, see cabinet painting.

Ceilings and trim are separate. Run the calculator again with the ceiling area. For the room as a whole, see what remodeling costs, or plan your remodel with us.

Questions this calculator answers

How many square feet does a gallon of paint cover?: It depends on the product. Benjamin Moore lists Benjamin Moore Regal Select interior, satin/pearl at 400–450 sq ft per gallon. Check the label of the paint you buy.
How do I work out wall area for paint?: Add the length of every wall, multiply by the height, and take off doors and windows.
How many coats of paint do I need?: The label for your product says. A big color change or a porous wall may need more than the label minimum.
Should I buy extra paint?: Round up to whole cans, and keep what is left for touch-ups. Buying it all at once keeps the tint consistent.

Sources and methodology

Figures dated October 22, 2026. Last reviewed August 16, 2026.

Regal Select Interior Paint, Satin/Pearl, product page (Benjamin Moore, retrieved October 22, 2026). Coverage 400–450 sq ft per gallon.
Lead Renovation, Repair and Painting Program (US Environmental Protection Agency, retrieved September 5, 2026). Certified firms for paint disturbed in pre-1978 homes.

Cabinet painting Painting cabinets, not walls.
Drywall calculator Sheets for new walls.
Bedroom remodel Where paint is most of the job.
Whole-home budget Paint as one line.

Plan Your Remodel Back to the home page