Roof pitch calculator
Convert a roof pitch between rise per 12, degrees, percent, and ratio, in either direction. Enter what you know and read the rest. Same math the CutOnce app runs on the jobsite.
Updated
Enter one measurement; the rest are the same pitch in other units.
- Rise per 12 (x/12)
- 6/12
- Angle
- 26.57°
- Slope percent
- 50%
- Ratio (rise/run)
- 0.50
- Rafter factor
- 1.1180
What roof pitch is
Roof pitch is the slope of the roof written as the rise in inches for every 12 inches of horizontal run. A 6/12 pitch rises 6 inches over 12 inches of run, which works out to 26.57 degrees or a 50 percent slope. Carpenters say it as “six twelve,” and it is the number a framing square, a rafter table, and a speed square are all built around.
A worked 6/12 example
One 6/12 pitch, shown in every unit. Every value below is computed by the same functions that drive the calculator above.
| Rise per 12 | 6/12 |
| Angle | 26.57° |
| Slope percent | 50% |
| Ratio | 0.50 |
| Rafter factor | 1.1180 |
Common roof pitches, converted
The pitches you meet most on residential work, from a low-slope 1/12 to a 45-degree 12/12. The rafter factor is the length of rafter per 1 inch of run: multiply your run by it to get line length.
| Pitch | Angle | Percent | Ratio | Rafter factor |
|---|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 0.08 | 1.0035 |
| 2/12 | 9.46° | 16.7% | 0.17 | 1.0138 |
| 3/12 | 14.04° | 25% | 0.25 | 1.0308 |
| 4/12 | 18.43° | 33.3% | 0.33 | 1.0541 |
| 5/12 | 22.62° | 41.7% | 0.42 | 1.0833 |
| 6/12 | 26.57° | 50% | 0.50 | 1.1180 |
| 7/12 | 30.26° | 58.3% | 0.58 | 1.1577 |
| 8/12 | 33.69° | 66.7% | 0.67 | 1.2019 |
| 9/12 | 36.87° | 75% | 0.75 | 1.2500 |
| 10/12 | 39.81° | 83.3% | 0.83 | 1.3017 |
| 12/12 | 45° | 100% | 1.00 | 1.4142 |
How to measure a roof's pitch
- 01
Level off 12 inches
Hold a level horizontal against a rafter or the roof surface and mark 12 inches along it from the low end. That 12 inches is your run, the same 12 every pitch is stated against.
- 02
Measure the rise at that mark
From the 12-inch mark, measure straight down to the roof. That vertical distance is the rise. Six inches down means 6/12. This is exactly what a speed square reads when you set it on a rafter.
- 03
Convert to whatever the job needs
Rise per 12 lays out cuts on a framing square, degrees sets a miter or a rafter-cutting jig, and percent is what drainage and accessibility specs are written in. They are the same slope in different clothes, which is what the calculator swaps between.
Common questions
- What is a 6/12 pitch in degrees?
- 26.57 degrees. A 6/12 rises 6 inches for every 12 inches of run, and the angle is the arctangent of 6 divided by 12. The other residential pitches: 4/12 is 18.43 degrees, 8/12 is 33.69 degrees, and 12/12 is exactly 45.
- How do I convert degrees back to a pitch?
- Take the tangent of the angle and multiply by 12. A 30-degree roof is tan(30) times 12, about 6.9/12. Set the calculator to degrees and it shows that exact conversion, 6.9/12, and you round to the common pitch you will cut, here a 7/12.
- What is the difference between pitch and slope?
- In everyday framing they are used for the same thing. Strictly, pitch is sometimes written as rise over the full span (rise/span) and slope as rise over run (rise/12). This calculator uses the rise-over-run convention carpenters actually cut to, the x/12 a framing square is marked in.
- What pitch counts as a low-slope roof?
- Anything below 2/12 is treated as low-slope and generally needs a membrane rather than shingles; most shingle manufacturers want 2/12 as the floor and special underlayment up to 4/12. Check the product's own instructions, since that is what a code inspector will.
Take the pitch to the cut list
Pitch is the first input to every rafter. The app carries it through to line length, the birdsmouth, ridge height, and a printable plan.
See also