Roofing Calculator

How to use this roofing calculator

1. Footprint unit, choose feet or metres for the building measurements.
2. Length and width, enter the footprint of the building (the area it covers on the ground).
3. Roof slope, pick the pitch that best matches your roof, from flat to steep.
4. Waste, set a percentage for offcuts and overlaps (12% is a sensible default).
5. Read your roof area, squares and bundles, they update instantly as you type.

Nothing is submitted or stored: the numbers never leave your device, so you can plan a job privately.

How to estimate roofing materials

The key idea is that a sloped roof always covers more surface than the ground it sits on. Start with thefootprint (length × width), then multiply by a slope factor to get the true roof area:roof area = footprint × slope factor. A flat roof uses a factor of 1.0, a medium pitch around 1.12, and a steep pitch about 1.25. If you measured in metres, the calculator converts to square feet first (1 m² = 10.764 sq ft).

Roofers count area in squares. A roofing square = 100 square feet, so a 2,000 square foot roof is 20 squares. Asphalt shingles are sold in bundles, and standard shingles come about 3 bundles per square, meaning one bundle covers roughly 33 square feet. To avoid running short, add a waste allowance of about 10-15% for cuts, starter rows, ridge caps and the offcuts around valleys and hips. This calculator applies your waste percentage before counting squares and rounds bundles up to whole packs.

Note: These figures are estimates for budgeting and planning. They assume a simple rectangular roof and standard 3-bundle shingles. Complex shapes, heavier shingles, underlayment, flashing and accessories are not included. Always have a roofer confirm the final order before you buy.

Frequently asked questions