Paint Calculator
Calculate how many gallons or liters of paint you need for a room.
What is the Paint Calculator?
This tool calculates the total wall area that needs paint, subtracts a standard allowance for doors and windows, and divides by your paint's coverage rate (and number of coats) to estimate how much paint to buy.
The formula
Wall area = 2 × (width + length) × height, minus 21 sq ft per door and 15 sq ft per window (standard average sizes). Gallons = (Paintable Area × Coats) ÷ Coverage per Gallon.
How to use it
- Enter your room's width, length and wall height.
- Enter the number of doors and windows.
- Enter how many coats you're applying and your paint's coverage rate (check the can — it's usually 350–400 sq ft per gallon).
Round up to the next full gallon when buying, and consider an extra 10% for touch-ups, textured walls, or a color change that needs an additional coat to fully cover.
Want the "why" behind this tool? Read Why the Paint Coverage Number on the Can Is a Best-Case Estimate.