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Rafter Length Calculator

Construction
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Calculates the length of a rafter based on the roof's span, rise, and overhang. This calculator helps ensure correct roof truss dimensions.

How To Use

How to use this calculator

Start with your values, or try a preset.

Step 1

Enter Roof Span (horizontal distance, in feet), Roof Rise (vertical distance, in feet), and Overhang (horizontal extension beyond the wall, in feet) in the units shown.

Step 2

Read Half Span (ft), Total Run (ft), and Rafter Length (ft) in the results panel. Results update as you change the inputs.

Step 3

Choose a preset to load an example, then adjust the values for your situation.

Worked Examples

Example calculations

See the inputs and their calculated results.

Small Shed

Roof Span (horizontal distance, in feet): 12 ft; Roof Rise (vertical distance, in feet): 3 ft; Overhang (horizontal extension beyond the wall, in feet): 1 ft

Half Span (ft): 6 ft; Total Run (ft): 7 ft; Rafter Length (ft): 7.615773106 ft

Standard Gable Roof

Roof Span (horizontal distance, in feet): 24 ft; Roof Rise (vertical distance, in feet): 6 ft; Overhang (horizontal extension beyond the wall, in feet): 1 ft

Half Span (ft): 12 ft; Total Run (ft): 13 ft; Rafter Length (ft): 14.31782106 ft

Steep Roof

Roof Span (horizontal distance, in feet): 20 ft; Roof Rise (vertical distance, in feet): 8 ft; Overhang (horizontal extension beyond the wall, in feet): 1 ft

Half Span (ft): 10 ft; Total Run (ft): 11 ft; Rafter Length (ft): 13.60147051 ft

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