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Rafter Length Calculator

Rafter length and pitch ratio from run and rise.

Compute the length of a roof rafter and the pitch ratio (rise per 12 inches of run) from the run and rise of the roof.

Nadia Almasri By Nadia Almasri
Published Last reviewed 1 min read

Inputs

ft
ft

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

Rafter length = √(run² + rise²). Pitch = rise × 12 / run (expressed as x/12).

In depth

Compute the length of a roof rafter and the pitch ratio (rise per 12 inches of run) from the run and rise of the roof.