Why roof area is bigger than the footprint
Because a pitched roof slopes, its surface is longer than the flat ground beneath it. Roof pitch is written as the rise (how far it climbs) over a run of 12 — so 6:12 rises six units for every twelve across. The steeper the pitch, the larger the multiplier, and the more material you need. A 6:12 roof, for instance, is about 1.12 times its footprint. Roofers often count in "squares," where one square equals 100 square feet of roof.
Frequently asked questions
How do I find my roof pitch?
Measure how many inches the roof rises over a level 12-inch run. That rise is the number you enter.
What is a roofing square?
A square is 100 square feet of roof surface — the unit most roofing materials are sold and quoted in.
Should I add extra for waste?
Yes — add about 10% for overlaps, ridges, hips and offcuts, and more for complex roofs.