Roof Pitch Calculator
Convert rise/run, X/12 pitch, roof angle, and slope percent with common and hip/valley factors. Use it free in the browser, or open the iPhone app for the same conversions on site.
Roof Pitch Calculator
Convert between pitch, angle, and slope percent. Optional run gives rafter lengths.
Pitch
- Roof angle
- Slope %
- Common rafter length
- Hip / valley length
- Common factor
- Hip / valley factor
App screenshots
Real Roof Pitch Calculator screens from the App Store listing.
How to use this calculator
- Pick the input mode that matches your field notes.
- Enter values in your chosen length unit for rise/run modes.
- Optional run length converts factors into common and hip/valley rafter lengths.
Features
- Pitch, angle, and slope % modes
- Common and hip/valley factors
- Rafter length from run
- Clear framing outputs
- Offline iPhone workflow
Formula
Pitch (in 12) = (rise ÷ run) × 12. Angle = arctan(rise ÷ run). Common rafter factor = √(1 + (pitch/12)²). Hip/valley factor = √(2 + (pitch/12)²).
6/12 pitch
Angle ≈ 26.57°, slope ≈ 50%, common factor ≈ 1.118, hip/valley factor ≈ 1.500 for a 12 in run reference.
Practical notes
- Hip/valley lengths assume square-corner plan geometry — adjust for actual layout.
Take it to the job site
Use Roof Pitch Calculator on your iPhone for fast repeat calculations and the full native workflow — wherever you're working.
Related calculators
Related guides
- How to Calculate Rafter Length — Work out common rafter length from span and pitch or rise and run.
- Roof Pitch to Rafter Length — Convert an X/12 pitch into rafter length for a known run.
- Common Rafter Formula — The core formula carpenters use for common rafter layout.
- Roof Pitch Explained — What X/12 pitch means and how it relates to angle.
FAQ
What is slope percent?
Vertical rise divided by horizontal run, expressed as a percentage (100% = 45°).
Pitch conversions are geometric — roofing material minimums and snow loads are separate checks.