Siding Squares

How this works

Siding is sold by the square — 100 SF, the same unit roofing uses — so this tool works the same basic way: gross wall area (perimeter × average wall height), plus any gable-end triangle area you add in separately, minus the total area of doors and windows to deduct, all divided by 100 and bumped up by a waste percentage.

Waste runs a bit higher for siding than for roofing, because horizontal or vertical lap coursing means every course has to be cut to fit around corners, openings, and trim, and off-cuts from one wall often can't be reused on the next. 10% covers a simple rectangular footprint; 15% is more realistic once there are multiple gables, dormers, or a lot of trim detail to work around — both numbers track what's commonly published in manufacturer install guides.

This tool doesn't try to auto-calculate gable-end area from a pitch, since gable shapes vary too much (full gable, half-gable, dutch gable) to reduce to one formula — enter that area directly if your walls have any, using length × height ÷ 2 for a simple triangular gable as a starting point.

Openings should reflect actual door and window sizes on the job, not an average — unlike the paint calculator, siding waste around openings is usually significant enough that a real measurement matters more than a shortcut.