Paint Calculator
Estimate interior wall paint volume from wall area, openings and coat count.
Calculate your materials
Your estimate
Enter your measurements and select Calculate estimate to see the results.
Estimates are for planning only; verify product specifications and local requirements.
How this paint calculator works
Paint coverage depends on the surface, the product and the number of coats. This calculator estimates gallons for equally sized wall sections, subtracts doors and windows, then applies the coverage rate from your paint label. Porous surfaces, heavy texture and dramatic color changes may require more.
The calculation
Paintable area = (wall length × wall height × number of walls) − door/window area. Total coverage = paintable area × coats. Gallons = total coverage ÷ coverage per gallon.
Worked example
Four 12 ft × 8 ft walls give 384 sq ft. Subtract 36 sq ft of openings for 348 sq ft. Two coats at 350 sq ft per gallon need about 1.99 gallons, or 2 whole gallons.
Before buying materials
- Measure walls individually if their lengths differ.
- Use the coverage range on the paint can, not an assumed universal rate.
- Keep a little extra for touch-ups when practical.
Frequently asked questions
Does this calculate ceilings?
This version estimates walls. For a ceiling, calculate its area separately and include it as another surface estimate.
Why choose two coats?
Many interior projects use two coats, but product and existing color determine actual needs.
Does primer count?
No. Estimate primer separately using the primer manufacturer’s stated coverage.