What this tool calculates
The wall area is the summed wall width multiplied by a shared height. Subtract only the opening area you choose to exclude. Multiply by the coat count, divide by the label’s square-foot coverage per gallon, and apply your chosen allowance.
The prefilled 350 sq ft per gallon and 10% allowance are example inputs, not a recommendation or a product performance claim.
Worked example
40 ft of wall width × 8 ft high − 20 sq ft of openings = 300 sq ft. Two coats at an example 350 sq ft per gallon with 10% extra require about 1.886 gallons. The supported purchase combination rounds to 2 gallon cans.
What is not included
Ceilings, primer, trim, texture-dependent performance and price optimization are not included unless separately accounted for. The smallest supported purchase volume is not necessarily the cheapest order.
Why the label matters: manufacturers publish coverage as a range that depends on surface texture and porosity, for example 400–450 sq ft per gallon for one premium interior paint (Benjamin Moore Regal Select 550 data sheet) and 350–400 sq ft per gallon for another (Ultra Spec 500 N538 data sheet). The number on your can, at the coat count its instructions call for, is the input to use. Our arithmetic example and interface are original project work.
Not sure what to measure? Read how to measure a room for paint, wallpaper and flooring.