Paint Calculations

To paint a room, calculate wall surface area: (perimeter × wall height) minus windows and doors. A 12 × 15 room with 8-foot ceilings has a perimeter of 54 feet, giving 54 × 8 = 432 sq ft of wall. Subtract ~40 sq ft for two windows and a door: 392 sq ft of paintable surface.

One gallon of paint covers about 350-400 sq ft with one coat. Two coats means you need roughly double. For the 392 sq ft room: 2 coats = 784 sq ft ÷ 375 sq ft/gallon ≈ 2.1 gallons. Buy 3 gallons to account for trim and touch-ups. This math prevents both shortage and waste.