Roof Pitch Calculator
Calculate roof pitch from rise and run, convert between pitch ratio, degrees, and slope percentage, and find rafter length. Essential for framing, roofing, gutters, and solar panel installation.
🏠 Roofing🏗️ Pitch = Rise / Run x 12 (inches of rise per 12 inches of run)
Rise (vertical, inches)
Run (horizontal, inches)
Rafter span (horizontal, ft)
Please enter valid values.
Formula & Reference
| Variable | Formula | Units |
|---|---|---|
| Roof Pitch Calculator | Pitch = Rise / Run x 12 (inches of rise per 12 inches of run) | ratio, degrees, % |
Step-by-Step Examples
Example 1
6/12 Standard Residential
Rise 6 in, Run 12 in.
- Pitch = 6/12
- Degrees = arctan(0.5) = 26.6
- Rafter mult = 1.118
- On 24-ft span: 12 ft x 1.118 = 13.42 ft rafter
✓ 6/12 pitch, 26.6 deg, rafter mult 1.118
Example 2
12/12 Steep Pitch
Rise 12 in, Run 12 in.
- Pitch = 12/12 = 45 degrees
- Very steep - safety equipment required
- On 28-ft span: 14 ft x 1.414 = 19.8 ft rafters
✓ 12/12 pitch = 45 degrees
Example 3
2/12 Low Slope
Rise 2 in, Run 12 in.
- Pitch = 2/12 = 9.5 degrees
- Too low for standard asphalt shingles (minimum 3/12 per most warranties)
- Requires modified bitumen, TPO, or EPDM flat roofing
✓ 2/12 pitch = 9.5 degrees (too low for shingles)
Real-World Applications
Roofing Contractors
Calculate rafter lengths and material quantities from pitch.
Material Estimating
Steeper roofs use significantly more shingles per plan sq ft.
Gutter Installation
Pitch determines downspout sizing and gutter slope requirements.
Framing
Carpenters use rafter multipliers to cut common, hip, and jack rafters.
Common Mistakes to Avoid
⚠️
Confusing run with span
Run is HALF the total width. If your house is 28 ft wide, the run is 14 ft, not 28 ft. Using the full span doubles your rafter length calculation.
⚠️
Measuring pitch on the slope
Always measure rise vertically and run horizontally. A level and tape measure is the correct tool - don't measure along the slope itself.
⚠️
Using shingles on a too-low slope
Minimum for asphalt shingles: 2/12 with special underlayment; 3/12 recommended minimum. Below 2/12, use only low-slope roofing products.
Frequently Asked Questions
What is roof pitch? ▾
Roof pitch is expressed as rise over run per 12 inches: a 6/12 pitch rises 6 inches for every 12 inches of horizontal distance. The higher the first number, the steeper the roof.
Most common US roof pitch? ▾
4/12 to 6/12. Ranch homes often use 4/12 (18.4 deg). Colonial and cape styles use 8/12 to 12/12. Steeper pitches (8/12-12/12) are common in snow country.
How does pitch affect shingle quantity? ▾
Use a pitch multiplier to convert plan area to actual roof area: 4/12 = 1.054x, 6/12 = 1.118x, 8/12 = 1.202x, 10/12 = 1.302x, 12/12 = 1.414x.
Minimum pitch for asphalt shingles? ▾
Minimum 2/12 with special installation per some manufacturers; 3/12 minimum per most warranties; 4/12 is the practical recommended minimum for long shingle life.
How to measure pitch from the ground? ▾
Use a smartphone pitch app, or hold a 12-inch level horizontal at the eave, then measure the vertical distance from the level to the roof surface.