Paint Calculator
Find out exactly how much paint you need for your project. Enter your wall dimensions, number of coats, and how many doors and windows to subtract, and we'll calculate the gallons and liters required.
Formula reviewed for accuracy. Our methodology & sources
Paint Calculator
construction calculator
How It Works
The calculator multiplies your total wall length by the height to get the gross area, then subtracts a standard allowance for each door and window so you are not paying to paint surfaces you will not cover. It multiplies the remaining paintable area by the number of coats and divides by a typical coverage of about 350 square feet per gallon, giving the gallons and liters to buy. Rough or porous surfaces and dramatic colour changes soak up more, so rounding up to the next can is sensible.
Formula
Paintable Area = (Wall Length × Height) − Doors − Windows Gallons = (Area × Coats) ÷ 350
Examples
40 ft walls, 8 ft high, 2 coats
About 1.6 gallons needed.
Frequently Asked Questions
How much does a gallon of paint cover?
One gallon of paint typically covers about 350 square feet with one coat. Coverage varies by paint type, surface texture, and color change.
How many coats of paint do I need?
Two coats is standard for most walls and gives the best, most even finish. You may need a third coat when covering a dark color with a lighter one.