Room/Wall Area Calculator
Calculate a room's floor area and net wall area after subtracting doors and windows.
About this calculator
Almost every paint, tile, wallpaper or plaster calculation starts with the same underlying number, net wall area, but getting there from raw room dimensions requires computing perimeter, multiplying by height, and then subtracting door and window openings, three separate steps that are easy to fumble by hand. This calculator multiplies room length and width to get floor area, computes gross wall area as twice the sum of length and width multiplied by wall height (the standard perimeter-times-height formula), then subtracts your entered door and window opening area to give the net wall area you'll actually paint, tile or plaster. Enter room dimensions, wall height and total opening area, and get floor area plus net wall area together instead of working through perimeter, multiplication and subtraction separately. Because this net figure feeds directly into paint, tile, plaster and wallpaper quantity calculations, getting it right here saves you from repeating the same subtraction across multiple other material estimates.
Worked example
12ft × 10ft room, 10ft height, 40 sqft of openings
Result: Net wall area = 400 sqft
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