Roofing & siding calculators

Estimating a roof or siding job

Every roofing estimate starts with the same number: the area of the roof surface, not the footprint of the house. The roof area calculator turns a footprint, pitch and overhang into square feet and roofing squares (one square is 100 square feet). The shingle, metal roofing and siding calculators then turn that area into what you actually buy: bundles, panels, trim and fasteners.

Waste depends on how cut-up the roof is. A simple gable roof typically needs about 10% extra shingles; hips, valleys and dormers push that toward 15% or more, because every cut at a hip or valley leaves an offcut. Starter strip and hip and ridge cap are counted separately from field shingles. Siding waste runs about 10% on plain walls and more on gables, where every course is cut at an angle.

Pitch matters because it stretches the footprint: a 6/12 roof has about 12% more surface than the flat area it covers, and a 12/12 roof about 41% more. The roof area calculator applies the pitch factor for you, and the shingle bundles chart lists the multiplier for every common pitch from flat to 24/12.

Measure from the ground or from plans where you can. Roofs steeper than about 6/12 are hard to walk safely, and flashing around chimneys and skylights, tear-off and ice-barrier rules at the eaves vary by region and by manufacturer. Use these numbers to order materials or to check a contractor’s quote, and confirm permit and underlayment requirements with your local building department before work starts.

How each calculator is specified, tested and corrected is described on our methodology page.