Rafter Calculator

Calculate rafter dimensions and cutting angles for your roof

Roof Specifications

Building Span (feet)

Roof Pitch (rise per 12")

Overhang (inches)

Rafter Spacing (inches)

Run (Horizontal)

12.00 feet

Rise (Vertical)

72.00 inches

Rafter Length

13.42 feet

Without overhang

Total Rafter Length

14.42 feet

With overhang

Roof Angle

26.57°

Birdsmouth Depth

3.50 inches

Rafters needed (40' building): 31

Total board feet (2×6): 447

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MyCalcBuddy Editorial Team

This page is maintained as an educational calculator reference.

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Formula Source: Standard Mathematical References

by Various

ðŸ”„Last reviewed: May 2026

âœ“Formula checks are based on standard references and internal QA review.