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Roof Rafter Span Calculator
Estimate rafter length from the run and pitch.
ruler Free Online Tool
⚡ Instant Results
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Rafter length
Compare Your Options And Get Clear Answers
Estimate rafter length from the run and pitch.
Roof Rafter Span Estimator
Enter your numbers below for an instant estimate.
0
💡 Tip: Add birdsmouth allowance separately.
How It Works
Key concepts behind this calculator
1
Enter Values
Fill in each field with your own numbers.
2
Calculate
Results update as you change the inputs.
3
Review
Read the breakdown and the explanation.
4
Adjust
Change values to compare scenarios.
Quick Reference Guide
Roof Quick Guide
Typical values for reference.
| Run | Pitch | Overhang | Length |
|---|---|---|---|
| 3 | 30 | 0.4 | 3.93 |
| 4 | 30 | 0.4 | 5.08 |
| 4 | 40 | 0.4 | 5.74 |
| 5 | 45 | 0.4 | 7.64 |
| Rule of Thumb | Check inputs | Use as a guide | Round sensibly |
Common Questions
Roof Rafter Span Calculator FAQ
Answers to common questions about this calculator.
See span tables.
It gives a quick estimate of roof rafter span from the values you enter.
No. It is a planning estimate, so check important figures with a professional or official source.
Yes. Edit any field and the result updates when you calculate.