How to Calculate Rafter Length
What is Rafter Length?
Rafter Length Calculator helps contractors and tradespeople accurately size, spec, and estimate materials and systems.
Formula
Rafter Length = √(Rise² + Run²) + Overhang
Step-by-Step Guide
- 1Use Pythagorean theorem with rise and run, add overhang
- 2Apply the formula using your project measurements
- 3Add required safety factors or waste allowances per code
Worked Examples
Input
8 ft rise, 16 ft run, 1.5 ft overhang
Result
Rafter = √(64+256) + 1.5 = 17.9 + 1.5 = 19.4 ft
Common Mistakes to Avoid
- ✕Not applying code-required safety factors or derating
- ✕Forgetting to account for waste and cut losses in material estimates
Ready to calculate? Try the free Rafter Length Calculator
Try it yourself →