Roofing Calculators
Work out roof pitch and shingle bundles needed for a re-roof or new build.
Calculators
Guides
Roof measurement basics
Every roofing estimate starts from the same two numbers: pitch (how steep the roof is) and footprint (the flat, ground-level area it covers). Pitch alone doesn't tell you how much material to buy, and footprint alone underestimates it — you need both.
Measure pitch first, from inside the attic if you can: hold a level horizontally against a rafter, mark 12 inches along it, and measure straight down to the rafter at that mark. That vertical distance in inches is your rise per 12 inches of run — the pitch. Measure footprint from the building's outer wall lines, including eave and rake overhangs, using a tape or the house's own plans. Neither measurement requires getting on the roof.
Pitch reference chart
Area multiplier converts a flat footprint into true sloped roof area — multiply your footprint by it to get the surface you'll actually cover in shingles, underlayment, and sheathing.
| Pitch | Angle | Area multiplier | Extra per 1,000 sq ft |
|---|---|---|---|
| 2/12 | 9.5° | 1.014 | 14 sq ft |
| 3/12 | 14.0° | 1.031 | 31 sq ft |
| 4/12 | 18.4° | 1.054 | 54 sq ft |
| 5/12 | 22.6° | 1.083 | 83 sq ft |
| 6/12 | 26.6° | 1.118 | 118 sq ft |
| 7/12 | 30.3° | 1.158 | 158 sq ft |
| 8/12 | 33.7° | 1.202 | 202 sq ft |
| 9/12 | 36.9° | 1.250 | 250 sq ft |
| 10/12 | 39.8° | 1.302 | 302 sq ft |
| 12/12 | 45.0° | 1.414 | 414 sq ft |
"Extra per 1,000 sq ft" is how much more shingle/underlayment area a 1,000 sq ft footprint needs at that pitch, compared to a flat roof of the same footprint. Exact figures for your own rise and run come from the Roof Pitch Calculator.
Which calculator do I need?
If you don't know your roof's slope yet — you're standing in the attic with a level, or reading numbers off an old plan — start with the Roof Pitch Calculator. If you already know the pitch (a contractor quoted it, or you calculated it previously) and just need a materials count, go straight to the Shingle Calculator; it asks for pitch as one of its inputs.
Roof Pitch → Shingle workflow
- Roof Pitch — Establish slope and the area multiplier from a rise/run measurement before ordering anything.
- Shingle — Apply that multiplier to the roof's footprint to convert flat area into bundles and squares, with waste factored in for hips, valleys, and starter courses.