How Much Paint Do You Need? The Room-by-Room Calculator Guide
One gallon covers 350-400 square feet. But walls have doors, windows, and closets. Here is the real math.
Step 1: Calculate wall area. Measure the perimeter of the room (add all four wall lengths) and multiply by the ceiling height. A 12×14 room with 8-foot ceilings: perimeter 52 feet × 8 = 416 square feet of wall area. Step 2: Subtract openings. Each standard door = 21 sq ft. Each standard window = 15 sq ft. A room with 1 door and 2 windows: 416 - 21 - 30 = 365 net square feet.
How Many Gallons
Most rooms need 2 coats. 365 sq ft × 2 coats = 730 sq ft of coverage needed. At 350 sq ft per gallon: 730/350 = 2.1 gallons. Buy 3 gallons — the extra lets you touch up later without worrying about color matching from a different batch. For ceilings: length × width = ceiling square footage. Same formula, but ceilings usually need only 1 coat if using ceiling paint (which is thicker).