Roof Rafter Calculator

Our premium pole barn kits come standard with pre-engineered trusses but building rafters is another viable DIY option for smaller span structures.

Our roof rafter calculator tools are handy for calculating the number of rafters needed, rafter length calculator, lineal feet of rafter, board feed in ridge and sub-facia,and the total board feet in the roof.

Rise and Run means that a 6/12 pitch roof has 6" of rise (vertical) for each foot of run (horizontal).

Rise / Run (in)
Approx Slope (degrees)
2/12 10°
3/12 14°
4/12 18°
5/12 23°
6/12 27°
7/12 30°
8/12 34°
9/12 37°
10/12 40°
11/12 42°
12/12 45°
Get exact slope using our
Roof Pitch Calculator.

Rafter Length Calculator
Building Width (FT) Beam Width (In) Overhang (In) Pitch (0-12)
ft in in /12


Trying to find what size lumber to use?
This is based upon the span of the rafter (horizontal span, not total rafter length), live and dead loads. To size joists and rafters use the Maximum Span Tables for southern yellow pine. This Rafter Span Calculator is species specific for Douglas Fir, hemlock, etc.

More Roof Calculators
Roof Truss Calculator
How To Cut Rafters


Next » Barn Doors

Kits for All Purpose Buildings

Gable • Raised Center Aisle / Monitor • Gambrel • Salt Shed • Mono-Slope
• Engineered Plans •