Paint Calculator
Calculate how many gallons of paint are needed to cover the walls of a room, accounting for doors, windows and coats.
About the Paint Calculator
This calculator estimates how much paint you need to cover a room's walls. It computes the total wall area from the room's perimeter and height, subtracts a standard allowance for doors (about 20 sq ft each) and windows (about 15 sq ft each), then divides by your paint's coverage rate — multiplied by the number of coats you plan to apply.
Formula: Wall Area = 2 × (Length + Width) × Height − Door/Window Deductions; Gallons = (Wall Area × Coats) ÷ Coverage per Gallon
Most paint covers about 350-400 sq ft per gallon on smooth walls. Buy a little extra for touch-ups, and remember darker colors or textured walls may need an extra coat.