Portal Frame Size Calculator
Enter the frame span, eaves height, and roof pitch to get a rough preliminary sizing estimate for a steel portal frame.
What this calculator does
This calculator gives a quick, rough sizing guide for a single-span steel portal frame, based on common structural rules of thumb used at the earliest concept stage of design.
How the calculation works
Rafter depth is estimated as roughly span ÷ 45, and column depth as roughly eaves height ÷ 12, which are commonly cited preliminary ratios for portal frame members. Ridge height adds the rise created by the roof pitch (span ÷ 2, multiplied by the tangent of the pitch angle) on top of the eaves height.
These are rough concept-stage figures only, meant for general planning and educational purposes. Final member sizes must always be confirmed by a qualified structural engineer using local codes, loading, and software analysis.