PaintBidPaint Calculator — How Many Gallons Do You Need?
Enter a room size (or a wall area you already know) and get the gallons you need — no guessing at the paint counter.
One gallon covers about 350 sq ft per coat on smooth walls. This calculator does the area math, multiplies by coats, and adds a sensible margin for touch-ups.
Painting the whole house — or hiring it out?
Gallons are only the material side. Contractors price labor, prep and markup on top. See how a full job is priced with the free painting estimate calculator for contractors, or check what an exterior job typically costs with the exterior painting cost calculator.
Frequently asked questions
How much paint do I need for a 12×12 room?
A 12 × 12 ft room with 8 ft walls has about 384 sq ft of wall area. One gallon covers roughly 350 sq ft per coat, so you need about 1.1 gallons per coat for the walls — buy 3 gallons for two coats and you will have touch-up paint left over. Add roughly 0.5 gallons per coat if you are painting the ceiling too.
How far does one gallon of paint go?
One gallon of latex paint covers about 350 sq ft in one coat on smooth, previously painted walls. On unpainted drywall, rough or porous surfaces, expect closer to 250–300 sq ft per gallon, and budget a primer coat as well.
Should I buy extra paint?
Yes — buy about 10% more than the exact calculation. It covers spills, heavier roller loading, and leaves you matched paint for future touch-ups, which matters because a new batch of the "same" color can dry slightly differently.
I am hiring a painter — is this the same math they use?
Contractors start from the same area-and-coverage math, then add labor, prep and markup to reach a quote. If you want to see the contractor side, the PaintBid estimate calculator prices a whole job room by room.