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Roof Pitch Calculator
Convert rise/run to angle and slope. Get the rafter multiplier in one click. Built by carpenters who use it every day on real job sites.
Common Pitches
Pitch
4.00/12
Angle
18.43°
Slope
33.3%
Rafter Mult.
1.0541
Rafter line length = run × 1.0541. For a 12″ run, that's 12.65″ of rafter.
Complete Pitch Reference Table
The 12 standard residential pitches with their angle, slope %, and rafter multiplier. Copy these values straight to a job site cheat sheet.
| Pitch | Angle | Slope % | Rafter Mult. |
|---|---|---|---|
| 1/12 | 4.76° | 8.33% | 1.0035 |
| 2/12 | 9.46° | 16.67% | 1.0138 |
| 3/12 | 14.04° | 25.00% | 1.0308 |
| 4/12 | 18.43° | 33.33% | 1.0541 |
| 5/12 | 22.62° | 41.67% | 1.0833 |
| 6/12 | 26.57° | 50.00% | 1.1180 |
| 7/12 | 30.26° | 58.33% | 1.1577 |
| 8/12 | 33.69° | 66.67% | 1.2019 |
| 9/12 | 36.87° | 75.00% | 1.2500 |
| 10/12 | 39.81° | 83.33% | 1.3017 |
| 11/12 | 42.51° | 91.67% | 1.3566 |
| 12/12 | 45.00° | 100.00% | 1.4142 |
How to Use a Roof Pitch
- 1
Measure rise and run
On an existing roof, measure 12 inches horizontal from where you want to start, then measure straight up to the underside of the roof. That vertical measurement is your rise.
- 2
Express as a ratio
Write it as rise:12. If you measured 6 inches up over 12 inches across, your pitch is 6/12.
- 3
Convert to angle if needed
Divide rise by run, take arctan. 6/12 = 0.5 → arctan(0.5) = 26.57°.
- 4
Use the rafter multiplier
For a 6/12 pitch, multiply your run by 1.1180 to get rafter line length. Add overhang × multiplier for total rafter length.
Frequently Asked Questions
What is roof pitch?
Roof pitch is the steepness of a roof, expressed as the rise (vertical) over the run (horizontal). It is most commonly written as inches of rise per 12 inches of run — so a "4/12" pitch rises 4 inches for every 12 inches of horizontal distance.
How do I convert pitch to degrees?
Take the rise divided by run and find the inverse tangent (arctan). For example, a 4/12 pitch is arctan(4/12) = 18.43°. The calculator above does this automatically.
What is the minimum roof pitch?
Most asphalt shingle manufacturers require a minimum 2/12 pitch. Below that, you need different materials: built-up roofing, modified bitumen, single-ply membranes (TPO/EPDM), or standing-seam metal can go as low as 1/4:12 or even flat.
What is the rafter multiplier?
The rafter multiplier converts horizontal run into rafter line length. For a 6/12 pitch, the multiplier is √(36+144)/12 = 1.1180. So a 12-foot run produces a 13.42-foot rafter line length.
What roof pitch is most common?
In residential construction, 4/12 to 8/12 is the most common range. Below 4/12 (low slope) is harder to shingle. Above 8/12 (steep slope) requires roof brackets, harnesses, and slows installation. The 6/12 pitch is the sweet spot for most U.S. homes.
How is slope percentage different from pitch?
Slope percent is just rise/run × 100. A 6/12 pitch is 50% slope. They describe the same angle differently. Engineers often use slope percent; carpenters use pitch ratio.
Need to Calculate Rafter Length Too?
Plug your pitch into our rafter calculator for full common, hip, and valley rafter dimensions including birdsmouth max depth.