Free rafter length calculator
Free online calculator. Enter roof dimensions. Calculate rafter length and see what to measure.
Run R is half the span for a symmetrical roof, or the full span for a mono-pitch roof. Measure H from the support reference level to the ridge and E horizontally beyond the support. Length is theoretical without ridge correction. Birdsmouth includes S, P, N and HAP. Cut line angles are measured to the long rafter edge.
Practical guides
Measurements, formulas and worked examples for your next project.
How to calculate rafter length from span and roof pitch
Measure span, rise and overhang correctly, then calculate a theoretical rafter length with a worked 8 m roof example.
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