About this calculator
Roof pitch describes steepness as inches of rise per 12 inches of horizontal run — a 6/12 roof climbs 6 in for every foot. This calculator converts any rise and run measurement into pitch, the roof angle in degrees, the percent slope and the pitch factor you multiply by to get rafter lengths and roof area.
How to use it
- Measure the rise: hold a level horizontally against the roof or rafter, mark 12 in along it, and measure straight down (or up) to the roof surface.
- Enter the run you measured along — 12 in if you used the method above.
- You can also enter the full rise and run of a rafter or gable, in any units.
- Read the pitch, angle and pitch factor.
The formula
Pitch = rise ÷ run × 12 (written as x/12)
Angle = arctan(rise ÷ run)
Slope % = rise ÷ run × 100
Pitch factor = √(1 + (rise ÷ run)²)
The pitch factor is how much longer a sloped surface is than its horizontal footprint. Multiply a rafter’s horizontal run by it to get the rafter length, or a footprint area by it to get roof area.
Worked example
These are the calculator’s starting values and the results they produce:
| Rise | 6 in |
|---|---|
| Run | 12 in |
Tips before you buy
- Common residential pitches range from 4/12 to 9/12. Pitches under 4/12 are “low slope” and usually need special underlayment or non-shingle roofing.
- Most asphalt shingle manufacturers require at least 2/12, with double underlayment between 2/12 and 4/12.
- Roofs steeper than about 7/12 generally need roof jacks or harnesses to work on safely.
- You can measure pitch from the attic on a rafter — it’s safer than climbing onto the roof.
Frequently asked questions
What angle is a 6/12 roof pitch?
A 6/12 pitch is 26.57°. Other common pitches: 4/12 is 18.43°, 8/12 is 33.69°, 12/12 is 45°.
How do I convert roof pitch to degrees?
Divide the rise by the run and take the arctangent. For 6/12, arctan(6 ÷ 12) = arctan(0.5) = 26.57°.
What is the pitch factor for a 6/12 roof?
√(1 + 0.5²) = 1.118. A 6/12 roof with a 1,000 sq ft footprint has about 1,118 sq ft of roof surface.
What is the most common roof pitch?
In the US, pitches between 4/12 and 9/12 are the most common on houses, with 6/12 a typical middle ground. Areas with heavy snow tend toward steeper roofs; low-slope roofs under 4/12 are common on porches, additions and modern designs.