Siding Calculator

About this calculator

Exterior siding is sold and installed by the square — a roofing and siding industry unit equal to 100 square feet of coverage — and packed into boxes that each cover a fixed area, typically listed on the product's spec sheet. Ordering exactly the wall area in siding almost always comes up short once cuts, overlaps, and mistakes are accounted for.

This calculator takes your total wall area, adds a waste percentage (commonly 10–15% for straightforward walls, more for complex cuts around windows and corners), and divides by the coverage per box to tell you how many squares and boxes to buy. Contractors estimating a job and homeowners planning a re-siding project use it to avoid both costly extra delivery trips and over-ordering material that goes to waste.