What this calculator does
This tool turns your measurements into a consistent planning estimate you can review before pricing or starting work. It is useful during early takeoffs, option comparisons, and on-site checks where transparent math matters.
How the calculation works
Formula
Paint = (wall area − openings) × coats ÷ coverage rate.Worked example
A 40 ft perimeter at 8 ft high, minus 40 ft² of openings, needs 560 ft² of coverage for two coats.
How to measure
- 01Measure total wall perimeter and finished wall height.
- 02Add door and window areas to subtract them.
Common mistakes to avoid
- Forgetting the second coat
- Using floor area as wall area
- Assuming label coverage applies to every surface
Limits of this estimate
Texture, porosity, colour change, application method, and waste affect coverage. Verify the product label.
Frequently asked questions
Should I subtract windows?
For a closer estimate, subtract their combined area. Many painters leave small openings in as a practical allowance.
What coverage should I use?
Use the manufacturer’s stated rate for the exact product and surface.