How Much Paint Do I Need?
Sherwin-Williams’ method is simple: divide the area by the coverage per gallon. For walls:
- Wall area = room perimeter × wall height, minus doors and windows.
- Gallons = wall area × coats ÷ coverage per gallon.
Worked example. A 12 × 10 ft room with 8 ft walls has 352 sq ft of wall. Take off a door (20 sq ft) and two windows (15 sq ft each) and 302 sq ft is left. Two coats at 350 sq ft a gallon is 1.73 gallons, so buy 2 gallons.
The calculator rounds to what you’d actually buy: whole gallons plus quarts for small remainders. Three quarts cost about as much as a gallon, so it rounds those up to a gallon.
Coverage per Gallon
HomeGuide puts typical coverage at 300–400 sq ft per gallon per coat. The real number is on the can and depends on:
- The surface. Bare drywall, textured walls, and masonry soak up more paint. Prime new drywall first.
- Color changes. Covering a dark color with a light one, or the reverse, can take an extra coat.
- How you apply it. Rollers with a thick nap hold more paint; sprayers use more.
Ceilings
Ceilings are usually painted with a flat ceiling paint, so the calculator counts them separately. Turn on Paint the ceiling too to add them.
What It Costs
Paint runs about $15–$50 a gallon (HomeGuide). A typical room needs about 1–2 gallons for the walls. Hiring a painter costs about $1–$3 a sq ft of wall.
Frequently Asked Questions
How Much Paint Do I Need for a 12 × 10 Room?
With 8 ft walls, one door, and two windows, there’s about 302 sq ft of wall. Two coats at 350 sq ft a gallon is 1.7 gallons, so buy 2 gallons.How Many Square Feet Does a Gallon of Paint Cover?
HomeGuide puts it at 300–400 sq ft per gallon for one coat. Sherwin-Williams says to check the product’s own coverage rate, which varies with the paint and the surface.How Many Coats of Paint Do I Need?
Two coats is the norm for interior walls. Big color changes, from dark to light or light to dark, can need a third coat or a primer.Sources
Prices are national ballparks checked October 2026. Local prices vary.