Roof Rafter Calculator
A rafter is a single sloped framing member, cut and installed on site rather than pre-built like a truss. This roof rafter calculator returns rafter length, roof angle, rise, and run — including your eave overhang — for stick framing or as a cross-check against truss designs.
Calculate Your Rafter Length & Angle
Enter your building specifications below. Results and the roof diagram update live as you type.
Live Roof Diagram
Results
Estimate Your Project Budget
Automatically calculated from your inputs above in the calculator.
Estimates only. Actual costs vary by region, supplier, and site conditions.
Truss vs Rafter Framing
A truss is a factory-built, triangulated assembly of top chords, bottom chords, and web members designed to span a full building width without interior support. A rafter is a single framing member, typically paired with ceiling joists or collar ties, cut and installed by a framing crew on site.
Rafters allow more flexible, open interior ceilings (cathedral or vaulted ceilings, for example) since there's no bottom chord forcing a flat ceiling line. Trusses are generally faster to install and more cost-effective for long, uninterrupted spans.
The rafter length shown in the calculator's results panel already accounts for your overhang — the eave extension beyond the wall — using the same rise-and-run geometry as the roof pitch calculator.
Frequently Asked Questions
Roof rafter calculator with overhang
Enter your overhang in inches above — the calculator adds it to the rafter length using the same roof pitch, so the eave extension is included automatically.
Rafter and roof pitch calculator
Rafter length is derived directly from your span and pitch inputs using the Pythagorean theorem; see the Pitch & Angle calculator for the underlying formulas.