Roofing Shingles Calculator

100 square feet of actual roof surface. It is the unit roofing is bought and sold in, so divide your roof area by 100 and that is what you order. The word 'actual' is doing real work there: it means roof surface, not the building footprint underneath.

3, for most 3-tab and architectural shingles, each bundle covering roughly 33 sq ft at typical exposure. Heavier architectural and designer lines are sometimes packed 4 to the square, which changes your count by a third. It is printed on the wrapper, so check before you order.

Measure the building footprint from the ground, length times width, then multiply by the slope factor for your pitch. A steeper roof holds more surface area than the ground it covers, and the slope factor is what converts between the two. The Roof Pitch Calculator works it out from your rise and run, and you can measure both from inside the attic if you would rather not go up.

10% on a simple gable. Closer to 15% on a hip roof, and 20% or more once you add valleys, dormers, or anything that forces angled cuts. Every valley is two cut edges, and the offcuts are rarely usable anywhere else.