Paint Coverage Calculator
Estimate how many gallons of paint you need for walls and ceilings. Account for doors and windows, multiple coats, coverage per gallon and an optional price per gallon.
Your paint estimate will appear here.
How much paint do I need?
Calculate the combined length of the walls to paint and multiply it by wall height. Subtract the total area of openings that will not be painted. Add a ceiling area if needed, then multiply by the number of coats. Finally, divide by the coverage printed on the paint can and round up to whole gallons.
Paint coverage formula
Net wall area = (combined wall length × wall height) − openings
Total coat area = (net wall area + ceiling area) × coats
Gallons needed = total coat area × (1 + allowance ÷ 100) ÷ coverage per gallon
Worked example
Suppose the combined wall length is 120 feet and wall height is 8 feet. Gross wall area is 960 square feet. Subtract 120 square feet for doors and windows to get 840 square feet. Two coats cover 1,680 square feet. At 350 square feet per gallon, that is 4.8 gallons before allowance; with 10% extra, plan for 5.28 gallons, or 6 whole gallons.
What changes paint coverage?
- Porous drywall, textured surfaces and unpainted plaster can absorb more paint.
- Colour changes, primer, sheen and paint formulation affect coverage.
- Brush and roller technique, overspray and surface condition can change actual consumption.
- Use the product label for the expected coverage and follow its preparation and recoat instructions.
Frequently asked questions
Does the calculator include primer?
No. Primer should be estimated separately using the product’s coverage and the areas that require priming.
Should I subtract doors and windows?
Enter their combined area if you do not intend to paint them. Small trim and reveals may still require paint.
Why round up gallons?
Paint is commonly purchased in standard container sizes. This estimate rounds up to whole one-gallon units; choose smaller cans where available if suitable.
Related estimators: Flooring Calculator · Tile Calculator · Roofing Calculator.
This is a planning estimate. Actual coverage depends on the surface, paint product and application. Follow the paint manufacturer’s label.