Calculator Inputs and Outputs
Inputs
- Horizontal seat-cut width (in) — example: 3.5
- Roof rise (in) — example: 6
- Roof run (in) — example: 12
- Rafter actual depth (in) — example: 7.25
Results
- Calculated vertical cut depth (in)
- Percent of rafter depth
- Common one-third limit (in)
- Depth check
Formula used
Vertical birdsmouth depth = horizontal seat width × roof rise/run.
How to Use the Rafter Birdsmouth Depth Calculator
Enter the requested values, check the units and assumptions, then select Calculate Rafter Birdsmouth Depth. The built-in defaults provide a complete working example.
Formula
Vertical birdsmouth depth = horizontal seat width × roof rise/run.
Understanding the Results
The primary answer appears first. Supporting outputs show related quantities, conversions, dates, costs, ratios, or intermediate values. Calculations keep additional precision before display rounding.
Accuracy Tips
- Use measured values and consistent units.
- Review assumptions, rates, timing, and efficiency inputs.
- Recalculate after changing any condition.
Important Note
This tool provides an informational estimate. Confirm critical financial, medical, construction, scientific, tax, legal, or safety decisions with an appropriately qualified professional.
Calculation Standards
This tool uses documented formulas and high-precision internal values. Displayed results may be rounded for readability. Review the assumptions and verify important decisions with a qualified professional.
Read our calculation methodology