Rafter Length
Use the Rafter Length for roofing planning. Enter Horizontal run (ft) and Vertical rise (ft) to get a clear result, formula explanation, and practical checks.
Rafter Length measurements
Enter your values, then calculate.
Result
How to calculate rafter length
This calculator finds rafter length using the Pythagorean theorem, from the horizontal run and vertical rise of a roof.
How the calculation works
Rafter length = √(Run² + Rise²).
Example
A run of 12 ft and rise of 6 ft: √(144+36) = √180 ≈ 13.4 ft.
Frequently asked questions
How is Result calculated?
Result = sqrt([Horizontal run] × [Horizontal run] + [Vertical rise] × [Vertical rise]).
Is the Rafter Length free to use?
Yes — every calculator on Simple Calculator Tools is free, runs in your browser, and does not require an account.
Rafter Length
Rafter length = √(Run² + Rise²).
Let's understand your rafter length result.
Calculate a result above and this guide will help you interpret it using this calculator's own formula and explanation.
Pro Tips for Rafter Length
- This gives the theoretical rafter length along the roof line — add extra for the overhang (eave) beyond the wall line, and account for birdsmouth cuts at the seat.
- Run is typically half the building width for a simple gable roof — confirm you're using half-span, not full span, unless your specific rafter spans the full width.
Common Rafter Length Mistakes to Avoid
- Using full building width instead of half-span (run) for a standard gable roof, which would significantly overstate the calculated rafter length.
When to Use This Calculator
This calculator finds rafter length using the Pythagorean theorem, from the horizontal run and vertical rise of a roof.