What is Roof Pitch?
Roof pitch is the steepness or slope of a roof, expressed as a ratio of the vertical rise to the horizontal run. In North America, pitch is typically stated as "X in 12" or "X/12," meaning the roof rises X inches for every 12 inches of horizontal distance. For example, a 6/12 pitch means the roof rises 6 inches for every 12 inches of run.
Roof pitch is a critical factor in roofing design because it affects water drainage, snow load capacity, material selection, and the overall aesthetic of a building. Building codes often specify minimum pitches for different roofing materials — for example, asphalt shingles generally require at least a 2/12 pitch.
Roof Pitch Formulas
Common Roof Pitches
| Pitch | Degrees | Slope % | Common Use |
|---|---|---|---|
| 1/12 | 4.8° | 8.3% | Near-flat, commercial |
| 2/12 | 9.5° | 16.7% | Low slope, minimum for shingles |
| 4/12 | 18.4° | 33.3% | Standard residential |
| 6/12 | 26.6° | 50.0% | Common residential |
| 8/12 | 33.7° | 66.7% | Steep residential |
| 10/12 | 39.8° | 83.3% | Very steep |
| 12/12 | 45.0° | 100% | Maximum standard |
How to Measure Roof Pitch
There are several ways to measure roof pitch:
- From the attic: Hold a level horizontally against a rafter, mark 12 inches along it, then measure vertically from the 12-inch mark to the rafter. That vertical measurement is your rise.
- From outside: Use a pitch gauge or digital level placed on the roof surface to read the angle directly.
- From measurements: If you know the total rise of the roof and the total run (half the span), divide rise by run and multiply by 12.
Worked Example
A roof that rises 8 inches for every 12 inches of horizontal run:
Angle = arctan(8/12) = 33.69°
Slope = (8/12) × 100 = 66.67%
Rafter per foot = √(8² + 12²) = 14.42 in
Frequently Asked Questions
What is the most common roof pitch?
The most common residential roof pitches range from 4/12 to 9/12. A 4/12 pitch is the minimum recommended for standard asphalt shingles without special underlayment, while 6/12 is very popular for its balanced appearance and good water shedding.
What is the minimum pitch for shingles?
The minimum pitch for standard asphalt shingles is 2/12, but pitches below 4/12 typically require additional underlayment. Some manufacturers specify 4/12 as their minimum for warranty coverage.
How do I convert pitch to degrees?
Use the formula: degrees = arctan(rise / run) × 180 / π. For example, a 6/12 pitch equals arctan(6/12) = arctan(0.5) = 26.57 degrees.
What pitch is considered a steep roof?
Roofs with a pitch of 8/12 or greater are generally considered steep. These roofs are more difficult to walk on and may require special safety equipment during installation and maintenance.