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This roof pitch calculator converts the rise and run of a roof into its pitch (such as 6/12), the angle in degrees, the slope as a percentage and the pitch multiplier used for roofing estimates. Add the horizontal run of a rafter and it also gives you the rafter length.
How to Use the Roof Pitch Calculator
- Measure the rise: the vertical height the roof climbs.
- Measure the run: the horizontal distance over which it climbs. A common method is to hold a level 12 in (or 30 cm) long against the roof and measure straight down to the roof surface at the end of the level.
- Enter both numbers in the same unit.
- Optionally enter the horizontal run of a rafter, from the outside of the wall to the center of the ridge, to get the rafter length.
Roof Pitch Formulas
Pitch = Rise ÷ Run × 12 (expressed as x/12)
Angle = arctan(Rise ÷ Run)
Slope % = Rise ÷ Run × 100
Pitch multiplier = √(1 + (Rise ÷ Run)²)
In the US and Canada, pitch is written as inches of rise per 12 inches of run, so a roof that rises 6 in for every 12 in has a 6/12 pitch. In the UK, Europe and Australia, roof slope is more often given in degrees.
Worked Example
- Rise 6 in, run 12 in: pitch = 6/12
- Angle: arctan(0.5) = 26.57°
- Slope: 50%
- Multiplier: √(1 + 0.25) = 1.118
- For a rafter with a 12 ft horizontal run: 12 × 1.118 = 13.42 ft before the overhang
Metric example: a roof that rises 1.5 m over a horizontal run of 4 m has a slope of 37.5%, an angle of 20.6° and a pitch of 4.5/12.
Roof Pitch to Degrees Chart
| Pitch | Degrees | Slope % | Multiplier |
|---|---|---|---|
| 1/12 | 4.8° | 8.3% | 1.003 |
| 2/12 | 9.5° | 16.7% | 1.014 |
| 3/12 | 14.0° | 25% | 1.031 |
| 4/12 | 18.4° | 33.3% | 1.054 |
| 5/12 | 22.6° | 41.7% | 1.083 |
| 6/12 | 26.6° | 50% | 1.118 |
| 7/12 | 30.3° | 58.3% | 1.158 |
| 8/12 | 33.7° | 66.7% | 1.202 |
| 9/12 | 36.9° | 75% | 1.250 |
| 10/12 | 39.8° | 83.3% | 1.302 |
| 12/12 | 45.0° | 100% | 1.414 |
Why Roof Pitch Matters
- Roofing material: asphalt shingles generally need at least a 2/12 pitch, with extra underlayment on low slopes. Flatter roofs need membrane systems.
- Cost: steeper roofs have more surface area and are slower and riskier to work on.
- Drainage and snow: steeper roofs shed water and snow faster.
- Usable attic space grows with pitch.
- Material estimates: the multiplier feeds straight into our roofing calculator.
Low, Conventional and Steep Slopes
Roofers often describe pitches below 4/12 as low-slope, 4/12 to 9/12 as conventional and above 9/12 as steep. Steep roofs usually need extra safety equipment and are priced higher per square.
Frequently Asked Questions
How do I find my roof pitch?
Place a level horizontally against the roof, measure 12 inches along it, and measure the vertical distance from that point down to the roof. That vertical distance is the rise per 12, which is your pitch.
What is a 6/12 roof pitch in degrees?
A 6/12 pitch is 26.57 degrees, a 50% slope, with a pitch multiplier of 1.118.
What is the most common roof pitch?
In North America, pitches between 4/12 and 9/12 are most common for houses, with 6/12 being a popular choice.
How do I convert roof pitch to degrees?
Divide the rise by the run and take the arctangent. For example, 4/12 gives arctan(0.333) = 18.4 degrees.
What is a pitch multiplier?
It is the factor that converts flat plan area into the real sloped roof area. Multiply the footprint (with overhangs) by the multiplier to get the roof surface area.
Related guide: Roof Pitch Explained: How to Measure It and Convert to Degrees
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