Roofing Calculator
Estimate the roof area and shingles needed.
From floor plan to roof area
A sloped roof is bigger than the floor beneath it. The steeper the pitch, the larger the slope factor. Multiply the footprint (including the overhang) by the slope factor to get the roof area.
Example
With the starting values shown (House length 40 ft; House width 30 ft; Roof pitch 6 in 12; Waste 10 %), Roof area comes out as 1,342. Other results include footprint: 1,200; slope factor: 1.118; roofing squares: 13.4.
This suits a simple gable or hip roof. Dormers, valleys, hips and ridge caps add waste, so ask a roofer for a measured quote. Bundles per square vary by product, so check the pack.
Frequently asked questions
What is a roofing square?
100 square feet of roof.
How much waste should I allow?
10% for a simple roof and 15% or more for a complex one.
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