Roof pitch calculator
Convert roof pitch to degrees, percent grade, slope ratio, and rafter factor. Enter a rise per twelve, or measure it in any unit.
Your roof
26.5651°≈
Multiply your run by 1.118034 for the rafter length. The cuts and the birdsmouth are in the app.
angle = atan(rise ÷ 12)
RUN 12" RISE 6" ANGLE 26.5651°
Roof pitch chart, 1/12 to 24/12
| Pitch | Angle | Grade | Factor |
|---|---|---|---|
| 1/12 | 4.7636° ≈ | 8.33% | 1.003466 |
| 2/12 | 9.4623° ≈ | 16.67% | 1.013794 |
| 3/12 | 14.0362° ≈ | 25.00% | 1.030776 |
| 4/12 | 18.4349° ≈ | 33.33% | 1.054093 |
| 5/12 | 22.6199° ≈ | 41.67% | 1.083333 |
| 6/12 | 26.5651° ≈ | 50.00% | 1.118034 |
| 7/12 | 30.2564° ≈ | 58.33% | 1.157704 |
| 8/12 | 33.6901° ≈ | 66.67% | 1.201850 |
| 9/12 | 36.8699° ≈ | 75.00% | 1.250000 |
| 10/12 | 39.8056° ≈ | 83.33% | 1.301708 |
| 11/12 | 42.5104° ≈ | 91.67% | 1.356568 |
| 12/12 | 45.0000° | 100.00% | 1.414214 |
| 13/12 | 47.2906° ≈ | 108.33% | 1.474317 |
| 14/12 | 49.3987° ≈ | 116.67% | 1.536591 |
| 15/12 | 51.3402° ≈ | 125.00% | 1.600781 |
| 16/12 | 53.1301° ≈ | 133.33% | 1.666667 |
| 17/12 | 54.7824° ≈ | 141.67% | 1.734054 |
| 18/12 | 56.3099° ≈ | 150.00% | 1.802776 |
| 19/12 | 57.7244° ≈ | 158.33% | 1.872684 |
| 20/12 | 59.0362° ≈ | 166.67% | 1.943651 |
| 21/12 | 60.2551° ≈ | 175.00% | 2.015564 |
| 22/12 | 61.3895° ≈ | 183.33% | 2.088327 |
| 23/12 | 62.4472° ≈ | 191.67% | 2.161854 |
| 24/12 | 63.4349° ≈ | 200.00% | 2.236068 |
Only 12/12 comes out clean. Every other row carries the ≈.
Use this roof pitch calculator to convert any roof pitch to its angle in degrees, its percent grade, its slope ratio, and its rafter factor. Pitch is written as rise per twelve inches of run — a 6/12 roof rises 6 inches for every foot of horizontal run. Enter your pitch and the calculator gives you all four values at once, or switch to MEASURE and enter a rise and run you took from the roof itself.
Roof pitch to degrees conversion
Builders talk in ratios; saws and digital angle finders need degrees. The conversion is one arctangent: roof angle = atan(rise ÷ 12). A 4/12 pitch comes out at 18.4349°, a 6/12 pitch at 26.5651°, and a 12/12 pitch is exactly 45°. Only 12/12 gives an exact angle; every other pitch produces an irrational number, so the calculator marks every answer except 12/12 with ≈ to show the value is rounded.
What is a good roof pitch for a shed?
Shed roof pitch depends on the roofing material. Asphalt shingles need at least 2/12, but most builders start at 3/12 for reliable drainage. Metal roofing can go as low as 1/12 with the right standing-seam profile. The same shed roof pitch calculator here handles all of them — pitch does not care about the building, only about the triangle in front of you.
Rafter factor and what it means for your cut list
The rafter factor (or roof pitch factor) is the number you multiply a horizontal run by to get the sloping length along the rafter. For a 6/12 pitch the rafter factor is 1.118034, so a 12 ft run gives a 13 ft 5-3/8 in common rafter, before the ridge deduction and overhang are counted. The formula is √(144 + P²) ÷ 12 — the hypotenuse of a right triangle 12 in wide and P in tall, expressed per foot of run.
Percent grade and slope ratio
Roof pitch has four common names, and which one you need depends on who is asking. Percent grade is rise ÷ run × 100 (a 6/12 roof is a 50% grade, the figure drainage and accessibility drawings call for). Slope ratio is written 1 : n (6/12 is 1 : 2). Degrees are what a saw blade trusts. All four appear together above so you never have to convert between them by hand.
How to measure roof pitch from inside or outside
From inside the attic, hold a level against the underside of a rafter, mark 12 inches along it from where it touches the rafter, and measure straight up to the rafter — that is your rise per twelve. From a ladder at the eave, the method is the same against the roof surface. From the ground, take a square-on photograph of the gable end and measure the rise and run on the image: pitch is a ratio, so scaling does not change the answer. Round to the nearest half inch before you type it — roofs are framed to whole and half pitches.
Questions about roof pitch
How do you calculate roof pitch?
Hold a level out twelve inches from the roof surface and measure straight down to it: that drop is the rise per twelve, so a 6 in drop is a 6/12 pitch. From any other pair of measurements the formula is pitch = rise ÷ run × 12.
What is a 4/12 roof pitch in degrees?
18.4349°, which is atan(4 ÷ 12). As a percent grade that is 33.33%, the slope ratio is 1 : 3, and the rafter factor is 1.054093.
What is a 6/12 roof pitch in degrees?
26.5651°. It is the most common residential pitch, its grade is 50.00%, and its rafter factor is 1.118034 — so a 12 ft run gives a 13 ft 5-3/8 in rafter.
What pitch is a 22.5 degree roof?
tan(22.5°) × 12 = 4.9706, so a fraction under 5/12. A true 5/12 pitch is 22.6199°.
What is the most common residential roof pitch?
Most houses sit between 4/12 and 9/12, and 6/12 is the pitch that turns up most often in stock plans. Below 3/12 you are into low-slope territory and shingles stop being the right covering.
What is the rafter factor?
The number you multiply a horizontal run by to get the length along the rafter. It is √(144 + P²) ÷ 12, where P is the rise per twelve. It saves you working the hypotenuse every time.
What is a shed roof pitch, and should it be different?
A shed roof has one slope and the pitch is calculated the same way. Shed roofs typically use pitches from 1/12 to 6/12 depending on the roofing material. The pitch matters more for drainage than headroom, but anything below 3/12 needs a low-slope covering.
How do I find the pitch of my roof from the ground?
Take a square-on photograph of the gable end, measure the rise and run on the image, and divide: pitch is a ratio, so scaling does not change the answer. Round to the nearest half-inch — roofs are framed to whole and half pitches.