Estimate roof rafter span, rafter line load, bending stress, shear stress, deflection, span ratio, and maximum allowable rafter span. Use this rafter span calculator for roof framing, rafters, shed roofs, gable roofs, roof joists, and preliminary structural planning.
Load conversion:
The calculator converts roof dead load, roof live load, and snow load in PSF into a rafter line load using rafter spacing.
Roof pitch:
The calculator estimates a slope factor from roof pitch and can use either plan-area load or sloped-area load.
Strength checks:
The calculator estimates bending stress and shear stress, then compares them to the entered allowable values.
Deflection check:
The calculator estimates rafter deflection and compares it to the selected span limit.
A rafter span calculator helps estimate whether a rafter size and spacing may be reasonable for a given roof span and roof load.
It can help compare rafter span, spacing, roof load, pitch factor, line load, bending, shear, deflection, and approximate maximum span.
Your result shows estimated rafter line load, total load, support reactions, maximum moment, bending stress, shear stress, deflection, allowable deflection, span ratio, and estimated maximum span. These are planning estimates only.
Rafter span is the distance a rafter runs between supports, such as a ridge beam, exterior wall, interior bearing wall, or roof beam.
Multiply roof load in PSF by rafter spacing in feet. For example, 35 PSF at 16 inches on center equals about 46.7 PLF before adding rafter self weight.
Yes. Roof pitch affects rafter length and may affect how loads are applied. This calculator includes a slope factor and lets you choose plan-area or sloped-area load basis.
No. Final rafter design should use approved span tables, species and grade values, roof load requirements, snow load requirements, bearing checks, local code requirements, and professional review when needed.