How the roofing calculator works
For a simple gable footprint, the calculator applies a slope factor based on rise per 12 inches, then adds your waste allowance and converts the result into roofing squares and bundles.
Example
A 6:12 roof uses a slope factor of about 1.118. A 40 × 28 ft footprint is therefore larger on the sloped roof surface than on the horizontal plan.
Important: this is a planning estimator for simple roof geometry. Valleys, hips, dormers, overhangs, starter courses, ridge caps, flashing, code requirements, and manufacturer instructions can materially change the order.
Roofing calculator FAQ
What is a roofing square?
One roofing square equals 100 square feet of roof area.
How many bundles are in a square?
Three is common for many products, but not universal. Enter the bundle count for the shingle product you are using.
Can I use this for a complex roof?
Split complex roofs into measured planes and confirm the final takeoff with a qualified roofer or supplier.