Roof Rafter Length and Pitch Calculator
Enter your roof's horizontal run and vertical rise to calculate the rafter length and pitch in standard x-in-12 notation.
Roof Rafter Length and Pitch Calculator
Calculates rafter length from run and rise, plus the roof pitch expressed in the standard x-in-12 notation.
This calculator treats the roof's run and rise as the two legs of a right triangle and applies the Pythagorean theorem to find the rafter length, then also converts the rise-to-run ratio into the standard x-in-12 pitch notation used throughout residential roofing. It's a quick way to check rafter cut lengths or communicate a roof's steepness using the notation contractors and building codes commonly reference, without needing a framing square calculation by hand.
Example
- With the default values shown above, this calculator returns: Rafter Length ≈ 4.272 m; Roof Pitch (x-in-12) ≈ 4.5-in-12.
Frequently Asked Questions
What does 'x-in-12' pitch notation mean?
It expresses how many units a roof rises vertically for every 12 units of horizontal run — a '6-in-12' roof rises 6 units for every 12 units across, a common way roofers describe steepness regardless of the actual units used.
How is rafter length calculated?
It uses the Pythagorean theorem, treating the run and rise as the two legs of a right triangle: rafter length = √(run² + rise²).
Sources
- Standard formula, publicly documented method