Rafter length calculator — from span, pitch and overhang

Enter the full building span in feet, the pitch as inches of rise per 12 inches of run, and the horizontal overhang. Results assume a symmetric gable with a single common rafter; ridge thickness deduction is not included.

IdiomaEnglish Français العربيةEspañolDeutsch Português Italiano 日本語

La herramienta y las etiquetas están en español. Las notas de referencia siguen en inglés.

rafter length calculator

Building span (ft)Pitch (rise per 12) (in/12)Horizontal overhang (ft)

Rafter length: 14.534ft
Length (ft-in): 14' 6.41"
Rise at ridge: 6ft
Roof angle: 26.57°

¿Necesitas un especialista certificado en CAD/BIM para modificar este archivo?

TaskBider drafters, detailers and BIM coordinators work remotely and every listing shows the pay. Typical published range for this work: $18–$45/hr.

Contrata a un delineante Publica este proyecto gratis

Formula

pitch factor = √(12² + pitch²) ÷ 12 · rafter = (span ÷ 2 + overhang) × pitch factor

Subtract half the ridge board thickness (measured level) from the run for a cut length. Confirm framing with your structural drawings.

Worked examples

Input	Result
24 ft span, 6/12, 1 ft overhang	13 × 1.118 = 14.534 ft (14' 6.41")
30 ft span, 4/12, no overhang	15 × 1.054 = 15.811 ft

Pitch factor (multiply run)

Pitch	Factor
3/12	1.0308
4/12	1.0541
5/12	1.0833
6/12	1.118
7/12	1.1577
8/12	1.2019
9/12	1.25
10/12	1.3017
12/12	1.4142

Questions

How do I calculate rafter length?

Take half the span plus overhang, then multiply by the pitch factor √(12² + rise²) ÷ 12.

Rafter length calculator — from span, pitch and overhang

rafter length calculator

¿Necesitas un especialista certificado en CAD/BIM para modificar este archivo?

Formula

Worked examples

Pitch factor (multiply run)

Questions

How do I calculate rafter length?

What is the pitch factor for 6/12?

Related tools

Popular CAD conversions

Related AEC calculators

File version help

Top freelance CAD & BIM engineers