What is roof pitch?
Roof pitch describes how steep a roof is. In the US it is written as the rise in inches for every 12 inches of horizontal run, so a 6/12 roof climbs 6 inches for each foot across. The same steepness can also be given as an angle in degrees or a percentage slope. This calculator converts between all of them.
How to measure your roof pitch
- From the roof: hold a level horizontally against the roof surface, mark 12 inches along the level, and measure straight up from that mark to the roof. That measurement is the rise.
- From the attic: do the same against the underside of a rafter.
- From the ground: measure the height of the ridge above the top of the walls (rise) and half the building width (run), then enter both in feet converted to inches, or just enter them in the same unit since only the ratio matters.
Roof pitch formulas
Angle (degrees) = arctan(rise ÷ run)
Slope % = rise ÷ run × 100
Multiplier = √(1 + (pitch ÷ 12)²)
Rafter length = (span ÷ 2 + overhang) × multiplier
Roof pitch chart
| Pitch | Angle | Slope | Typical use |
|---|---|---|---|
| 1/12 | 4.8° | 8.3% | Flat roofs, membrane |
| 3/12 | 14.0° | 25% | Porches, sheds, metal roofing |
| 4/12 | 18.4° | 33.3% | Ranch homes |
| 6/12 | 26.6° | 50% | Most common for houses |
| 8/12 | 33.7° | 66.7% | Colonial, cape homes |
| 12/12 | 45.0° | 100% | Steep, Tudor and Victorian styles |
Worked example
A garage is 24 ft wide and the ridge sits 6 ft above the top of the walls. The run is half the width, 12 ft. Pitch = 6 ÷ 12 × 12 = 6/12, an angle of 26.6°. Each rafter spans 12 ft horizontally plus a 12 inch overhang, so its length along the slope is 13 × 1.118 = about 14 ft 6 in before cuts.
Once you know the pitch, use the roofing calculator to work out squares and shingle bundles.
Frequently asked questions
What is a 6/12 roof pitch in degrees?
A 6/12 pitch is about 26.57 degrees, a 50% slope. It is the most common pitch on American houses.
How do I calculate roof pitch?
Divide the rise by the run and multiply by 12. A roof that rises 4 feet over a 12 foot run has a 4/12 pitch.
What is the minimum pitch for shingles?
Most asphalt shingle makers require at least 2/12, with special double underlayment between 2/12 and 4/12. Below 2/12 you need a low-slope membrane roof.
What is a 12/12 roof pitch?
A 12/12 roof rises 12 inches for every 12 inches across, which is a 45 degree angle and a 100% slope. Its surface area is about 41% larger than its footprint.
How do I find rafter length from pitch?
Take half the building span plus the overhang, then multiply by the pitch multiplier, √(1 + (pitch ÷ 12)²). For a 24 ft span, 12 inch overhang and 6/12 pitch: 13 × 1.118 = 14.5 ft.
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Last updated October 2026.