Question 1

Why is the roof area bigger than the building footprint?

Accepted Answer

A sloped roof has more surface area than the flat footprint below it — the steeper the pitch, the bigger the difference. This tool multiplies the plan (footprint) area by a pitch-specific factor to estimate the actual sloped area that needs covering.

Question 2

What is a "roofing square"?

Accepted Answer

A square is the roofing industry's unit of coverage, equal to 100 square feet of finished roof area. Materials — shingles, underlayment, and labor — are commonly priced and ordered by the square, which is why this calculator converts your area into squares alongside bundles.

Question 3

How many bundles of shingles are in a square?

Accepted Answer

Standard three-tab and most architectural asphalt shingles are packaged three bundles to a square, which is the assumption used here. Some heavier architectural or designer shingles use four or five bundles per square — check your product’s coverage specs and adjust the bundle count accordingly.

Question 4

How much extra should I add for wastage?

Accepted Answer

A simple gable roof typically needs 10% extra for cuts, overlaps, and starter/ridge courses. Roofs with more hips, valleys, dormers, or a steep pitch usually need 15–20% to account for the additional cutting and waste at each feature.

Roofing Material Estimator

Footprint to sloped area

Common questions