Calculator Inputs and Outputs
Inputs
- Common-rafter horizontal run (ft) — example: 12
- Roof rise per 12 run (in) — example: 6
- Tail or overhang along valley (ft) — example: 1
- Waste allowance (%) — example: 5
Results
- Valley rafter length (ft)
- Valley horizontal run (ft)
- Vertical rise (ft)
Formula used
For equal roof pitches, valley horizontal run = common run × √2; rafter length uses the Pythagorean theorem.
How to Use the Valley Rafter Length Calculator
Enter the requested values, check the units and assumptions, then select Calculate Valley Rafter Length. The built-in defaults provide a complete working example.
Formula
For equal roof pitches, valley horizontal run = common run × √2; rafter length uses the Pythagorean theorem.
Understanding the Results
The primary answer appears first. Supporting outputs show related quantities, conversions, dates, costs, ratios, or intermediate values. Calculations keep additional precision before display rounding.
Accuracy Tips
- Use measured values and consistent units.
- Review assumptions, rates, timing, and efficiency inputs.
- Recalculate after changing any condition.
Important Note
This tool provides an informational estimate. Confirm critical financial, medical, construction, scientific, tax, legal, or safety decisions with an appropriately qualified professional.
Calculation Standards
This tool uses documented formulas and high-precision internal values. Displayed results may be rounded for readability. Review the assumptions and verify important decisions with a qualified professional.
Read our calculation methodology