Roofing
Roof Pitch Calculator
Enter a rise and run, a pitch such as 6/12, or an angle to get the roof pitch, angle in degrees, slope percent and slope factor. Add the footprint to estimate the roof surface area.
How we calculate
Roof pitch compares how far a roof rises with how far it runs on the level. In the U.S. it is written as inches of rise per 12 inches of run, so a roof that climbs 6 inches over 12 inches is a 6 in 12 (or 6/12) roof. The same ratio works in any unit, which is why metric measurements give the same pitch.
OSHA uses the same notation in its construction fall-protection rules: a low-slope roof is “a roof having a slope less than or equal to 4 in 12 (vertical to horizontal)” and a steep roof is one “having a slope greater than 4 in 12”. We show which group your roof falls in. Source: OSHA 29 CFR 1926.500(b), definitions.
The roof area estimate assumes every roof plane has the same pitch. For roofs with mixed pitches, dormers or valleys, work out each section separately.
Worked example
A 6 in 12 roof over a 1,500 sq ft footprint:
- Ratio: 6 / 12 = 0.5
- Angle: arctan(0.5) = 26.57 degrees
- Slope factor: square root of (6^2 + 12^2) / 12 = 13.4164 / 12 = 1.11803 (shown as 1.118)
- Roof surface: 1,500 x 1.11803 = 1,677.05 sq ft
Measured in the attic: a rise of 4 in over a 12 in level is a 4 in 12 roof: 18.43 degrees, slope factor 1.054, and a low-slope roof by the OSHA definition.
| Pitch | Angle (degrees) | Slope factor |
|---|---|---|
| 2 in 12 | 9.46 | 1.014 |
| 3 in 12 | 14.04 | 1.031 |
| 4 in 12 | 18.43 | 1.054 |
| 5 in 12 | 22.62 | 1.083 |
| 6 in 12 | 26.57 | 1.118 |
| 7 in 12 | 30.26 | 1.158 |
| 8 in 12 | 33.69 | 1.202 |
| 9 in 12 | 36.87 | 1.25 |
| 10 in 12 | 39.81 | 1.302 |
| 12 in 12 | 45 | 1.414 |
How to measure pitch from the ground or the attic
- In the attic: hold a level flat 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 per 12.
- From plans: many house plans print the pitch next to the roof, for example 6/12.
- From a gable end: if you know the height of the roof peak above the wall top and half the building width, enter them as rise and run.
Stay off the roof
This page does not give advice on working on a roof. OSHA sets fall-protection rules for roofing work in construction; if work is needed up there, hire a qualified roofing contractor.
What you need to measure
- Tape measure
- A level (a 12 in or 24 in level makes the math easy)
- Pencil and notepad
- House plans, if you have them
- The footprint area, from plans or the square footage calculator
FAQ
What does a 6/12 roof pitch mean?
The roof rises 6 inches for every 12 inches of level run. That is an angle of 26.57 degrees and a slope of 50 percent.
How do I convert roof pitch to degrees?
Divide the rise by 12 and take the arctangent. For example 8 in 12: arctan(8 / 12) = 33.69 degrees. The table above lists common pitches.
What is a slope factor?
It is how much longer the sloped roof surface is than its level run: square root of (rise^2 + run^2) divided by run. Multiply a flat footprint area by it to estimate the roof surface area.
Is a 4/12 roof steep?
Not by OSHA’s definition. Its construction rules call a roof with a slope of 4 in 12 or less a low-slope roof, and anything greater than 4 in 12 a steep roof.
Can I use metric units?
Yes. Switch to Metric and enter the rise and run in centimeters. Pitch is a ratio, so the result is the same; we show the angle and slope percent first.
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Estimates only. Results are estimates based on the measurements you enter. Check local building codes and your product labels, confirm quantities with your supplier, and buy a little extra material. This is not professional or structural advice. Roof pitch results are geometry only: they do not tell you which roofing products or structure suit your roof. Check product instructions and local code. Last checked: September 27, 2026.