Roofing
Roof pitch, slope & rafters
Every roofing estimate hangs on one number, and it's the one most people can't quote off the top of their head: the pitch. Pitch is simply rise over run - how far the roof climbs for every 12 units it travels horizontally, written as 6:12, or expressed as an angle in degrees or a percent slope. A low 4:12 roof is a gentle walk; a 12:12 is a steep 45°.
That angle matters because a sloped roof always covers more surface than the flat footprint beneath it - and the steeper the pitch, the bigger the gap. This tool turns your pitch into a pitch multiplier and applies it to the building's footprint, so you get the true roof area to order shingles against. Measure from the ground or the attic where you can; there's no reason to climb a steep roof with a tape.
Guides
Frequently asked questions
What is roof pitch, and how is it written?
Pitch is the roof's steepness, measured as rise over run: the vertical rise for every 12 units of horizontal run. A “6:12” roof rises 6 for every 12 across, which works out to about 26.6° or a 50% slope. Low-slope roofs run 3:12 to 4:12, 6:12 is a common medium pitch, and 12:12 is a steep 45°. You can read it off a level and tape without climbing up.
How do I find my roof's area without climbing on it?
You don't measure the sloped surface directly - you measure the footprint (the flat outline of the building plus overhangs) from the ground, then multiply by the pitch multiplier. Footprint × multiplier gives the true roof area. Read the pitch off a level held against a rafter in the attic, or a phone angle app, and let the calculator do the rest.
What is a “pitch multiplier”?
It's the factor that converts flat footprint area into actual sloped area. Geometrically it's √(rise² + run²) ÷ run - for a 6:12 roof that's about 1.12, so the roof surface is 12% larger than the ground it covers. A 4:12 adds around 5%; a steep 12:12 (45°) adds a full 41%. Skip it and you'll under-order every time.
How much extra roofing material should I buy?
Add roughly 10% waste on a simple gable roof, and 15% on a hip roof or anything with lots of valleys, dormers and cuts. Shingles are sold by the “square” (100 sq ft, about 9.3 m²), so round up to whole bundles. Keep a few spare - matching the color and batch years later is nearly impossible.