Roof Rafter Calculator
Calculate rafter length and birdsmouth setback from span, pitch and overhang.
Estimate only — not a substitute for a licensed tradesperson, a certified engineer, or sign-off from your local building surveyor. Verify against current standards and site conditions before ordering materials or starting work.
Result
- Run (half span + overhang)
- 4,450mm
- Rafter length
- 4,816.65mm
- Indicative birdsmouth depth (1/3 rafter depth guide)
- 30mm
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What this is based on
Geometry - rafter length from span and pitch. Rafter SIZING is a span-table matter and is deliberately not attempted here.
We cite the clause and link to the publisher so you can read the source yourself. We do not reproduce the text or tables of the NCC or of any Australian Standard.