Rafter Length Calculator

Enter the rafter run (ft) and the angle of the rafter (degrees) into the Rafter Length Calculator. The calculator will evaluate the Rafter Length. 

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Rafter Length Formula

The following two example problems outline the steps and information needed to calculate the Rafter Length.

RL = R / cos(a)

• Where RL is the Rafter Length (ft)
• R is the rafter run (ft) 
• a is the angle of the rafter (degrees) 

How to Calculate Rafter Length?

The following example problems outline how to calculate Rafter Length.

Example Problem #1:

1. First, determine the rafter run (ft). 
   • The rafter run (ft) is given as: 30.
2. Next, determine the angle of the rafter (degrees). 
   • The angle of the rafter (degrees) is provided as: 50.
3. Finally, calculate the Rafter Length using the equation above: 

RL = R / cos(a)

The values provided above are inserted into the equation below and computed.

RL = 30 / cos(50deg) = 46.67 (ft)

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Example Problem #2: 

For this problem, the variables required are provided below:

rafter run (ft) = 40

angle of the rafter (degrees) = 20

Test your knowledge using the equation and check your answer with the calculator..

RL = R / cos(a) = ?