Span-to-Depth Sizing Calculator

Get a preliminary depth range for a beam from its span - a starting point only. Enter your span and support condition below to get a rough sense of how deep the beam is likely to need to be, before you pick an actual catalogued section and run it through the real checks.

Unlike the other calculators on this site, this tool is not based on an AISC 360 or ASCE 7 clause - there's no code formula for "what depth should I start with". This is general rule-of-thumb guidance only. Treat the result as a first guess, never a final answer.
Scope of this tool:
  • This is a preliminary sizing aid only - it does not check bending, shear, or deflection capacity. That's what the Beam Analysis module is for, once built.
  • The ratios are typical, commonly-used figures, not a mandated standard - treat the suggested range as a starting point, not a target to hit precisely.
  • Composite ratios assume the beam acts compositely with a concrete slab via shear studs. If you haven't decided on composite action yet, use the non-composite ratios as the more conservative (deeper) starting point.
This calculator provides preliminary, indicative structural calculations only, intended to assist with initial sizing and understanding. It is not a substitute for assessment by a qualified structural engineer, and cad-steel.com accepts no responsibility for its use in any final design.