Rafter Length and Ridge Rise Calculator
Calculate common rafter length and rise to ridge from building span, roof angle and horizontal overhang.
Formula
Planning estimate. Check product specifications and local requirements before purchasing.
Worked example: Rafter Length Calculator
Measurements in this example
| Building span | 8 m |
|---|---|
| Horizontal overhang | 0.5 m |
| Roof angle | 30 ° |
Calculated quantities
| Rafter length | 5.2 m |
|---|---|
| Rise to ridge | 2.31 m |
What to check
This calculation uses: Building span, Horizontal overhang, Roof angle. It returns: Rafter length, Rise to ridge.
The result is geometric length only. Seats, ridge cuts, birdsmouth, fascia allowance and connection details remain to be designed.
Verify the roof structure, loads and cutting layout with a qualified designer before altering or fabricating structural members.
Use the units beside each field. The values in the worked example are starting inputs; replace them with your measurements and the specifications of your material.
Compare alternatives
Open a tool, enter your measured dimensions, then save an estimate. Keep another version if you want to compare products or allowances.