Rafter Calculator
Counts rafters along building length direction simplified as span/spacing +1.
Step 1: Units
Step 2
Enter project measurements
Use decimals if needed (e.g. 3.5).
How to use this calculator
Enter plan dimension along ridge and rafter spacing.
What the math is doing
Counts rafters along building length direction simplified as span/spacing +1.
Frequently asked questions
Hip roofs?
This is a ridge-run simplification only.
Birdsmouth?
Does not change count.
Collar ties?
Separate members.
Engineering?
Follow truss or rafter tables.