Paint Calculator – How Much Do You Need?

A standard 12×12 room with 8-foot ceilings, one door, and one window has about 348 sq ft of paintable wall area. At 350 sq ft per gallon that's roughly 1.0 gallon per coat, so two coats need about 2.0 gallons. Buy 3 gallons to cover the 10% waste margin. Change the room size, ceiling height, or number of coats to get a precise figure for your space.