Formula
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
- Common rafter geometric line only; ridge deduction, birdsmouth, plumb cuts and member sizing excluded.
Example Calculation
- Horizontal wall-to-ridge run: 3 m
- Horizontal eave overhang: 0.5 m
- Roof angle: 30 °
A 3 m run plus 0.5 m horizontal overhang at 30° gives a 4.0415 m line length.
Frequently asked questions
How do I use this calculator?
Enter horizontal wall-to-ridge run, horizontal eave overhang, roof angle. The result updates automatically. Use Reset to restore the example values.
What method does it use?
rafter line length=(run+horizontal overhang)/cos(angle).. Common rafter geometric line only; ridge deduction, birdsmouth, plumb cuts and member sizing excluded.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.