Roof Pitch Calculator
Find roof pitch from rise and run, or from an angle, with the pitch in x/12, the angle in degrees, the slope percentage, the rafter factor and the rafter length.
Results
| Item | Value |
|---|
Quick Answer
Roof pitch is how many inches the roof rises for every 12 inches it runs. A roof that rises 6 inches over 12 inches is a 6/12 pitch, which is an angle of 26.57° and a slope of 50%. To find the pitch from any rise and run, divide the rise by the run and multiply by 12.
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Table of Contents
- Roof Pitch Calculator
- Quick Answer
- Related Calculators
- How This Roof Pitch Calculator Works
- How to Use the Roof Pitch Calculator
- Roof Pitch Formulas
- Key Terms
- Worked Example
- Real-Life Examples
- Roof Pitch vs Roof Slope and Angle
- Roof Pitch Chart
- How to Measure Roof Pitch
- Common Mistakes to Avoid
- Frequently Asked Questions
- References & Sources
How This Roof Pitch Calculator Works
Choose what you know: the rise and run, the pitch, or the angle. The calculator works out the other measures: the pitch as x in 12, the angle in degrees, the slope as a percentage and the rafter factor. Add the run of one side of the roof in feet to get the height of the ridge above the wall and the rafter length.
Quick explanation: a 6/12 pitch means the roof rises 6 inches for every 12 inches across.
- Rise: the vertical height the roof climbs.
- Run: the horizontal distance it covers.
- Rafter factor: multiply the run by it to get the sloped rafter length.
How to Use the Roof Pitch Calculator
- Choose whether you know the rise and run, the pitch, or the angle.
- Enter the values, picking the unit for rise and run.
- Optionally, enter the run of one roof side in feet for the rafter length.
- Press Calculate.
- Read the pitch, angle, slope, rafter factor and lengths.
Roof Pitch Formulas
- Pitch: rise ÷ run × 12 (inches of rise per 12 inches of run)
- Angle: arctan(rise ÷ run)
- Pitch from angle: tan(angle) × 12
- Slope percent: rise ÷ run × 100
- Rafter factor: √(1 + (rise ÷ run)²); rafter length: run × factor
Key Terms
- Pitch: the rise of a roof in inches for each 12 inches of horizontal run.
- Rise: the vertical height from the top of the wall to the ridge.
- Run: the horizontal distance from the outside of the wall to below the ridge.
- Span: the full width covered by the roof, twice the run on a simple gable.
- Rafter factor: the number you multiply the run by to get the sloped length of a rafter.
Worked Example
You measure a roof that rises 5 ft over a run of 10 ft.
- Rise ÷ run = 5 ÷ 10 = 0.5
- Pitch = 0.5 × 12 = 6/12
- Angle = arctan(0.5) = 26.57°
- Rafter length = 10 × √(1 + 0.5²) = 11.18 ft before the overhang
Real-Life Examples
- Shed roof: a rise of 2 ft over 8 ft is a 3/12 pitch, or 14.04°.
- Rafter order: a 24 ft wide house with an 8/12 roof has a run of 12 ft and rafters of 12 × 1.2019 = 14.42 ft before the overhang.
- From an angle: a 30° roof is a pitch of 6.93/12, close to 7/12.
- Ridge height: a 6/12 roof over a 14 ft run rises 7 ft above the wall top.
Roof Pitch vs Roof Slope and Angle
- Pitch is written as rise in 12, such as 6/12. It is the usual way US builders describe roofs.
- Slope as a percentage is rise ÷ run × 100, so 6/12 is a 50% slope.
- Angle is measured in degrees from horizontal: 6/12 is about 26.57°. A 12/12 roof is 45°.
Roof Pitch Chart
| Pitch | Angle | Slope | Rafter factor |
|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.0035 |
| 2/12 | 9.46° | 16.7% | 1.0138 |
| 3/12 | 14.04° | 25.0% | 1.0308 |
| 4/12 | 18.43° | 33.3% | 1.0541 |
| 5/12 | 22.62° | 41.7% | 1.0833 |
| 6/12 | 26.57° | 50.0% | 1.1180 |
| 7/12 | 30.26° | 58.3% | 1.1577 |
| 8/12 | 33.69° | 66.7% | 1.2019 |
| 9/12 | 36.87° | 75.0% | 1.2500 |
| 10/12 | 39.81° | 83.3% | 1.3017 |
| 12/12 | 45.00° | 100.0% | 1.4142 |
| 14/12 | 49.40° | 116.7% | 1.5366 |
| 16/12 | 53.13° | 133.3% | 1.6667 |
| 18/12 | 56.31° | 150.0% | 1.8028 |
How to Measure Roof Pitch
The safest way is from inside the attic. Hold a level against the underside of a rafter, mark a point 12 inches along the level, and measure straight up from that mark to the rafter. That number is the pitch. From outside, you can measure the rise and run of a gable end from the ground with a tape and a level, or use a smartphone angle app on a rafter tail. Do not climb onto a steep or wet roof to measure it.
Roofing materials have minimum pitches. Many asphalt shingle makers ask for at least 2/12, with extra underlayment below 4/12. Flat and low-slope roofs usually need membrane roofing. Check the instructions for your material.
Common Mistakes to Avoid
- Using the full span as the run. On a gable roof, the run is half the span.
- Mixing units. Rise and run must be in the same unit before you divide.
- Confusing pitch with angle. A 6/12 pitch is about 26.6°, not 6°.
- Forgetting the overhang. Add the overhang length to the rafter length.
- Measuring on the roof surface. Run is measured level, not along the slope.
Frequently Asked Questions
Divide the rise by the run and multiply by 12. A 4 ft rise over 12 ft is 4/12.
About 26.57 degrees.
Many US houses have pitches between 4/12 and 9/12.
45 degrees, because the rise equals the run.
Take the tangent of the angle and multiply by 12. 30° is about 6.93/12.
Usually a roof below about 3/12 or 4/12, which often needs special roofing.
Multiply the run by the rafter factor, then add the overhang.
Rise ÷ run × 100. A 6/12 pitch is a 50% slope.
Yes. A steeper roof has more surface area for the same footprint; multiply the footprint by the rafter factor.
References & Sources
| Source | Used For | Link |
|---|---|---|
| OpenStax, Algebra and Trigonometry 2e, 7.2 Right Triangle Trigonometry | Tangent and the Pythagorean theorem used for angle and rafter length. | https://openstax.org/books/algebra-and-trigonometry-2e/pages/7-2-right-triangle-trigonometry |