Rafter Length Calculator (Angle & Pitch)
This calculator helps you find the length of a rafter using either the roof angle or the pitch. Just input the vertical rise, roof run, and angle or pitch value to compute the accurate rafter length for roof framing — ideal for carpenters, roofers, and structural engineers.
Calculate Rafter Length from Roof Angle or Pitch
Rafter Length Formulas
$$\text{Rafter Length} = V + \frac{R}{2 \cdot \cos(A)}$$
$$\text{Rafter Length} = V + \frac{R}{2} \cdot \sqrt{1 + P^2}$$
Where
- $$V$$ — vertical rise (e.g., ridge height)
- $$R$$ — roof run (horizontal span)
- $$A$$ — roof angle (in degrees)
- $$P$$ — pitch = rise/run
This calculator provides two methods: one using the roof angle with trigonometry (cosine), and the other using the pitch ratio. Both are essential in building sloped roofs, gables, or dormers. Accurate rafter lengths reduce cutting errors and material waste on site.