Interior
How to Calculate Paint for a Room
Estimate wall area, subtract openings, account for coats, and convert paint coverage into gallons.
Open Paint CalculatorCalculate wall area
For a rectangular room, add length and width, multiply by two, then multiply by wall height. This gives the wall area before doors and windows.
Subtract openings
Subtract typical door and window areas for a closer estimate. This matters more in rooms with large windows, multiple doors, or built-in openings.
Apply coats and coverage
Multiply paintable area by the number of coats, then divide by the paint's coverage per gallon. Round up so there is enough paint for touch-ups.
Use The Calculator With This Guide
This guide explains the measuring method, while the Paint Calculator turns the same measurements into project quantities, waste-adjusted results, and a copyable shopping list. Use the guide first when you are deciding what to measure, then use the calculator when you are ready to compare material amounts.
Open Paint CalculatorMeasurement Checks
- Forgetting the second coat.
- Assuming every paint covers the same area.
- Subtracting openings twice or using unrealistic door/window areas.
Formula Reference
Wall area = 2 × (length + width) × wall_height
Paintable area = wall_area - door_area - window_area
Gallons = paintable_area × coats / coverage_per_gallon
Adjusted gallons = gallons × (1 + waste_factor)
FAQ
Should primer count as a coat?
Primer is usually planned separately. Use the paint calculator for finish paint, then estimate primer with the primer label's coverage.
Why does color change affect paint quantity?
High contrast color changes can require extra coats, which increases gallons needed.