How much paint do I need?

A simple way to work out how many gallons a job needs — by surface area, coverage rate and number of coats — so you never over- or under-buy.

Start with the surface area

Paint is bought by coverage, so you need square feet of surface. For walls, multiply total wall length by ceiling height. Subtract large openings (big windows, doors) if you want to be precise; many painters leave them in as a safety margin.

Know your coverage rate

A gallon of wall paint typically covers about 350–400 sq ft in one coat on smooth, previously painted drywall. Rough, porous or previously unpainted surfaces drink more, so coverage drops.

Multiply by the number of coats

Divide your surface area by the coverage rate to get gallons per coat, then multiply by the number of coats (usually two). Add primer separately if you're covering a big color change, bare surface or stains.

Don't forget trim, ceilings and waste

Ceilings, trim, doors and windows use different products and cover at different rates — estimate them separately. Add roughly 5–10% for waste, touch-ups and what stays in the tray and roller.

Or let WEDO do the math

WEDO estimates surfaces, coats and paint from a photo, so you quote materials and labor without hand math. Try the free calculator to see it work.

FAQ

How much does a gallon of paint cover?

Usually about 350–400 square feet in one coat on smooth, previously painted drywall. Rough or porous surfaces cover less.

How much paint to paint a room?

Measure the wall area, divide by ~375 sq ft per gallon, then multiply by your number of coats. A 12×12 room usually needs about 1.5–2 gallons for two coats of wall paint, plus ceiling and trim.