Rafter Length Calculator

Formula

To calculate the rafter length (\(RL\)):

\[ RL = \frac{R}{\cos(a)} \]

Where:

\(RL\) is the rafter length (ft)
\(R\) is the rafter run (ft)
\(a\) is the angle of the rafter (radians)

What is a Rafter Length?

The rafter length is the distance from the top of the wall to the peak of the roof, along the slope of the rafter. It is an essential measurement in construction and carpentry for determining the length of the rafter needed to support the roof structure.

Example Calculation 1

Let's assume the following values:

Rafter Run (\(R\)) = 10 ft
Rafter Angle (\(a\)) = 0.785 radians (45 degrees)

Using the formula:

\[ RL = \frac{10}{\cos(0.785)} \approx \frac{10}{0.707} \approx 14.14 \text{ ft} \]

The rafter length is approximately 14.14 ft.

Example Calculation 2

Let's assume the following values:

Rafter Run (\(R\)) = 15 ft
Rafter Angle (\(a\)) = 0.523 radians (30 degrees)

Using the formula:

\[ RL = \frac{15}{\cos(0.523)} \approx \frac{15}{0.866} \approx 17.32 \text{ ft} \]

The rafter length is approximately 17.32 ft.