What this calculator does
Estimate paint quantity from wall area, openings, coats, coverage, and waste allowance.
How it works
The calculator evaluates paint = [perimeter × height − openings] × coats × (1 + waste%) ÷ coverage. Inputs are checked before calculation, and invalid values such as zero denominators or out-of-range selections produce a clear error instead of a misleading result.
Input query strings and outputs
Use an input name in this page’s URL as ?name=value, and join additional inputs with &. Portable shared links may instead use the compact ?ac= state parameter.
Input query strings
7-
?roomLength=Room lengthNumber · Required · Default: 15
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?roomWidth=Room widthNumber · Required · Default: 12
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?wallHeight=Wall heightNumber · Required · Default: 8
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?openingsArea=Doors and windows areaNumber · Required · Default: 40
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?coats=Number of coatsNumber · Required · Default: 2
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?coverage=Coverage per gallon (ft²)Number · Required · Default: 350
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?wastePercent=Waste allowanceNumber · Required · Default: 10
Outputs
4-
gallonsPaint required (gallons)Number · Primary output
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gallonsToBuyWhole gallons to buyWhole number
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paintAreaCoated area (ft²)Number
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netWallAreaNet wall area (ft²)Number
Inputs and results
The inputs are Room length, Room width, Wall height, Doors and windows area, Number of coats, Coverage per gallon (ft²), Waste allowance. Results include Paint required (gallons), Whole gallons to buy, Coated area (ft²), Net wall area (ft²).
Important notes
This is a planning estimate. Product coverage and surface conditions can materially change actual paint use.