Roof pitch explained
"6/12" tells a roofer almost everything about a roof's steepness. Here's what the numbers mean, how to measure them and why they change how many shingles you need.
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What roof pitch means
Roof pitch (or slope) is written as rise over run: how many inches the roof rises for every 12 inches it runs horizontally. A 6/12 roof rises 6 inches for every foot. The higher the first number, the steeper the roof.
| Pitch | Angle | Description |
|---|---|---|
| 2/12–3/12 | 9.5°–14° | Low slope; shingles need special underlayment |
| 4/12–6/12 | 18.4°–26.6° | Common, walkable with care |
| 7/12–9/12 | 30.3°–36.9° | Steep; roof jacks or a harness needed |
| 12/12 | 45° | Very steep, typical of A-frames and some Victorian roofs |
How to measure pitch
- From the attic (safest): hold a level horizontally against the underside of a rafter, mark 12 inches along the level, and measure straight up from that mark to the rafter. That measurement is the rise.
- From a ladder at the gable: do the same against the rake board at the edge of the roof.
- With your phone: many inclinometer and pitch-gauge apps read the angle when you lay the phone on a rafter or photograph the gable end.
Why pitch changes the amount of material
A sloped roof has more surface than the footprint it covers. The pitch factor converts one into the other: multiply the footprint (including overhangs) by the factor to get the real roof area. A 6/12 roof has 11.8% more surface than its footprint; a 12/12 roof has 41% more.
Example: a 30 × 40 ft footprint
- At 4/12: 1,200 × 1.054 = 1,265 sq ft
- At 8/12: 1,200 × 1.202 = 1,442 sq ft — about 1.8 squares (5 or 6 bundles) more than the 4/12 roof
The roofing calculator applies the factor automatically and turns the area into squares and bundles.
Pitch limits for roofing materials
- Asphalt shingles aren't used below 2/12. Between 2/12 and 4/12, manufacturers and the building code require extra measures such as double underlayment.
- Low-slope roofs below 2/12 need membrane roofing (for example EPDM, TPO or modified bitumen).
- Metal roofing has its own minimum slopes depending on the panel and seam type.
Frequently asked questions
What is the most common roof pitch?
Many US homes have roofs between 4/12 and 9/12, with 6/12 being very common.
Is a 4/12 roof walkable?
Generally yes with good footwear and dry conditions. Anything steeper than about 7/12 needs roof jacks or fall protection.
How do I convert pitch to degrees?
Take the arctangent of rise ÷ 12. For 6/12: arctan(0.5) = 26.6°.