How roof pitch is measured
Pitch is the rise in inches for every 12 inches of level run, written 6/12 or 6:12. A 6/12 roof climbs 6 inches for every foot it runs in from the eave toward the ridge.
Under the roof
In the attic, hold a level across the underside of a rafter with one end touching it. Mark 12 inches along the level and measure straight up from that mark to the rafter. That measurement is the rise.
On the roof
From a ladder at the eave or rake, set one end of a level on the roof, hold it level, and measure from the 12 inch mark down to the roof surface. A phone's level laid on the roof reads the angle instead; enter it under Angle.
From the gable end
Measure the building's width wall to wall and the height of the ridge above the top of the walls. The run is half the width, so a 24 foot wide house with the ridge 6 feet up is 6 over 12, a 6/12 pitch.
The math behind the numbers
Every figure comes from the rise and the run:
Angle = arctan(rise ÷ run)Slope as a percent = rise ÷ run × 100Roof area factor = √(rise² + 12²) ÷ 12Hip and valley factor = √(rise² + 288) ÷ 12The roof area factor is how much longer the slope is than the level run. Multiply a roof's flat area, the footprint inside its edges, by it to get the area on the slope. At 6/12 the factor is 1.118, so 1,200 sq ft of footprint carries 1,342 sq ft of roof. At 12/12 it is 1.414: the roof has 41% more area than the ground it covers.
The hip and valley factor gives the length of a hip or valley where both roof planes share one pitch. Multiply the common rafter's run, half the building's width, by it. A 6/12 hip roof on a 24 foot wide house has hips of 12 × 1.500 = 18 feet, before overhangs.
The common rafter without its overhang is the run times the roof area factor: 12 × 1.118 = 13.42 feet, or 13' 5", for that same house.
Roof pitch chart
Angles, slopes and factors for the common pitches, worked out with the formulas above.
| Pitch | Angle | Slope | Area factor | Hip and valley |
|---|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 | 1.417 |
| 2/12 | 9.46° | 16.7% | 1.014 | 1.424 |
| 3/12 | 14.04° | 25.0% | 1.031 | 1.436 |
| 4/12 | 18.43° | 33.3% | 1.054 | 1.453 |
| 5/12 | 22.62° | 41.7% | 1.083 | 1.474 |
| 6/12 | 26.57° | 50.0% | 1.118 | 1.500 |
| 7/12 | 30.26° | 58.3% | 1.158 | 1.530 |
| 8/12 | 33.69° | 66.7% | 1.202 | 1.563 |
| 9/12 | 36.87° | 75.0% | 1.250 | 1.601 |
| 10/12 | 39.81° | 83.3% | 1.302 | 1.641 |
| 11/12 | 42.51° | 91.7% | 1.357 | 1.685 |
| 12/12 | 45.00° | 100.0% | 1.414 | 1.732 |
| 14/12 | 49.40° | 116.7% | 1.537 | 1.833 |
| 16/12 | 53.13° | 133.3% | 1.667 | 1.944 |
| 18/12 | 56.31° | 150.0% | 1.803 | 2.062 |
| 24/12 | 63.43° | 200.0% | 2.236 | 2.449 |
Common questions
What is a 6/12 roof pitch in degrees?
26.57 degrees. The angle is arctan(6 ÷ 12). A 4/12 roof is 18.43 degrees, an 8/12 roof 33.69 and a 12/12 roof exactly 45.
What is the lowest pitch for asphalt shingles?
2/12. The International Residential Code (section R905.2.2) allows asphalt shingles only on slopes of 2/12 or more, and from 2/12 up to 4/12 they go over two layers of underlayment. Flatter roofs take a low-slope membrane such as modified bitumen, TPO or EPDM.
Which pitches count as steep?
Pitched roofs on houses mostly run from 4/12 to 9/12. Insurance estimates commonly add a steep charge from 7/12, with higher brackets from 10/12 and above 12/12, because those roofs need roof jacks, harnesses and slower work.
Is pitch the same as slope?
In roofing today, yes: both mean rise over 12 inches of run. Slope is sometimes written as a percent instead, so a 6/12 slope is 50%. Older framing books defined pitch as rise over the full span, which makes a 6/12 roof a 1/4 pitch. The angle is the same roof in degrees.
How does pitch change the materials?
Shingles, underlayment and labor follow the area on the slope, not the footprint. Multiply the footprint by the roof area factor, or use the roofing calculator, which does that and counts squares, bundles, drip edge and ridge cap.