Construction & Home
Paint Calculator
This calculator estimates how many gallons of paint you'll need based on the wall area you're covering and how many coats you plan to apply.
The formula
wall area = length × height
gallons needed = (wall area × coats) ÷ 350
Worked example
A wall 40 ft long and 9 ft high, painted with 2 coats:
wall area = 40 × 9 = 360 sq ft
gallons needed = (360 × 2) ÷ 350 = 2.06 gallons
Frequently asked questions
How much wall area does a gallon of paint cover?
A standard gallon of paint typically covers around 350 square feet with one coat, though coverage can vary by paint brand, wall texture, and surface porosity — check your paint can's label for the exact coverage rating.
Should I subtract doors and windows from the wall area?
For a more precise estimate, yes — subtract the square footage of large doors and windows before calculating. This calculator uses the full wall area, so treat the result as a slightly generous estimate if your walls have a lot of openings.
Why does the number of coats matter so much?
Paint needed scales directly with the number of coats — two coats roughly doubles the paint required compared to one, since you're covering the same wall area multiple times.