Rafter Length Calculator
Calculate common rafter length from run, pitch and overhang.
Estimate
How to use this calculator
Enter your project measurements and allowances. The estimate updates instantly. Round ordering quantities up and confirm product coverage with your supplier.
Formula
Rafter length = horizontal run × √(12² + rise²) ÷ 12.
Planning tip
Field conditions, cuts, overlaps, compaction and local building requirements can change actual material needs. Use this result as a planning estimate and verify critical structural details with a qualified professional.
Frequently asked question
Should I include waste?
Yes. Most projects need extra material for cuts, breakage, irregular layouts and measurement differences. The appropriate allowance depends on the product and project.