Roof Pitch Ratio Calculator – Angle, Factor & Chart
Calculate roof pitch angle and multiplier factor for any pitch ratio. Reference chart for common roof slopes from 1/12 to 12/12.
in
in
sq ft
Common Roof Pitch Ratios
| Pitch | Angle | Factor |
|---|---|---|
| 1/12 | 4.76° | 1.003 |
| 2/12 | 9.46° | 1.014 |
| 3/12 | 14.04° | 1.031 |
| 4/12 | 18.43° | 1.054 |
| 5/12 | 22.62° | 1.083 |
| 6/12 | 26.57° | 1.118 |
| 7/12 | 30.26° | 1.158 |
| 8/12 | 33.69° | 1.202 |
| 9/12 | 36.87° | 1.250 |
| 10/12 | 39.81° | 1.302 |
| 11/12 | 42.51° | 1.357 |
| 12/12 | 45.00° | 1.414 |
Roof Pitch Ratios Formula
Pitch Factor = √(Rise² + Run²) / Run | Angle = arctan(Rise / Run)
How to Calculate Roof Pitch Ratios
- 1. Determine the rise (vertical) and run (horizontal) in inches
- 2. Calculate the pitch factor: √(Rise² + Run²) ÷ Run
- 3. Calculate the angle: arctan(Rise ÷ Run) in degrees
- 4. If you have a base area, multiply by pitch factor for actual roof area
Example Calculation
Let's say you're calculating the pitch for an 8/12 roof with a 1,000 sq ft base area.
- rise: 8
- run: 12
- baseArea: 1000
Pitch ratio is 8/12, angle is 33.69°, pitch factor is 1.202. Actual roof area for 1,000 sq ft base = 1,202 sq ft
Tips
- A 4/12 pitch rises 4 inches for every 12 inches of horizontal run
- Pitches from 4/12 to 9/12 are considered standard for residential roofs
- The pitch factor tells you how much extra roofing material you need compared to flat area
- Low-slope roofs (below 4/12) require special waterproofing membranes
Frequently Asked Questions
What does a 5/12 roof pitch mean?
A 5/12 pitch means the roof rises 5 inches vertically for every 12 inches of horizontal distance. This equals approximately 22.62 degrees with a pitch factor of 1.083.
What is the angle of an 8/12 roof pitch?
An 8/12 roof pitch has an angle of approximately 33.69 degrees with a pitch factor of 1.202.
How do I read a roof pitch chart?
A roof pitch chart shows the ratio (rise/run), the corresponding angle in degrees, and the pitch factor/multiplier. Higher ratios mean steeper roofs with larger pitch factors.