This works out how much paint a wall needs, subtracting doors and windows and accounting for multiple coats.
How it works
Paint needed
gallons = (wall area − openings) × coats ÷ coverage per gallon
Coverage varies by product and surface — commonly 300–400 ft² per gallon for a smooth interior wall, but your specific can’s label is the authoritative figure for that product.
Why openings get subtracted
A single door is roughly 20 sq ft; three doors and two windows on one wall can be 10% or more of that wall’s total area. Ignoring openings is not a small rounding error at typical room sizes — it visibly overstates the paint needed.
How to use this calculator
- Enter the total wall area to paint.
- Subtract the area taken up by doors and windows.
- Set the number of coats and check your paint can’s own coverage figure.
Frequently asked questions
Why isn’t there one universal coverage number?
Because it genuinely depends on the product and the surface — a textured wall soaks up more paint than a smooth one, and different paint formulations spread differently. The number on your specific can is more accurate than any general rule.
Do I need two coats for every job?
Not always — a single coat can be enough over a similar existing colour with a quality paint. A colour change, especially to or from a dark colour, usually needs two coats for even coverage.
Should I paint the ceiling too?
This calculator handles wall area only — run the ceiling as a separate calculation if you’re painting it, since ceiling paint sometimes has different coverage characteristics.
Why does the result round up to eighths of a gallon?
Because paint is commonly sold in increments down to a pint (⅛ gallon) at the low end — rounding the exact calculated amount up to the next available size is more useful than a raw decimal you can’t actually buy.
What if I’m using a paint-and-primer-in-one product?
The same formula applies — just use that product’s own stated coverage rate, since combined products sometimes cover slightly less per gallon than paint alone.
