Common Rafter Length Calculator

To calculate the common rafter length, square the rise and run of the roof, then add these values together. Finally, take the square root of the sum to get the rafter length.

Common Rafter Length Calculator

Enter any 2 values to calculate the missing variable

Run of the Structure

Inches (in) Feet (ft) Centimeters (cm) Meters (m)

Rise of the Roof

Inches (in) Feet (ft) Centimeters (cm) Meters (m)

Common Rafter Length

Inches (in) Feet (ft) Centimeters (cm) Meters (m)

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A Common Rafter Length Calculator is a tool used to calculate the length of a rafter based on the rise and run of the roof. This tool simplifies the process of determining rafter length and is commonly used in roofing projects. The calculator can also accommodate different roof pitches, making it an essential tool for professionals and DIYers alike.

Formula:

$$CRL = \sqrt{(RS^2) + (RL^2)}$$

Variable	Description
CRL	Common Rafter Length
RS	Rise (Vertical height of the roof)
RL	Run (Horizontal length of the roof)

Example Calculation:

Let’s say the Rise (RS) is 3 meters and the Run (RL) is 4 meters.

Using the formula:

$$CRL = \sqrt{(RS^2) + (RL^2)} = \sqrt{(3^2) + (4^2)} = \sqrt{9 + 16} = \sqrt{25} = 5 \text{ meters}$$ 

So, the common rafter length is 5 meters.

Step	Calculation	Result
1	Square the Rise (RS)	$3^2 = 9$
2	Square the Run (RL)	$4^2 = 16$
3	Add the squared values	$9 + 16 = 25$
4	Find the square root of the sum	$\sqrt{25} = 5$ meters

What is the Common Rafter Length Calculator?

A common rafter length calculator is a useful tool for determining the length of rafters used in pitched roofs. For example, to calculate the rafter length for a 4/12 pitch roof (where the rise is 4 inches for every 12 inches of run), the calculator computes the total rafter length based on the roof’s pitch and span.

The rafter length table provides predefined values for various roof pitches and spans, making it easier to look up lengths without doing manual calculations. Using a rafter length calculator with birdsmouth also accounts for the cutout at the base of the rafter where it rests on the top plate.

For larger spans like a 12-foot span, the size and material of the rafter will depend on factors like the roof pitch and load. These calculators also help ensure you choose the right size and spacing between rafters to provide adequate support for the roof structure.

Additionally, the rafter calculator app offers a quick way to calculate lengths on-site, providing instant results based on the roof’s rise and run values.