Span-to-Depth Sizing Calculator

Get a preliminary depth range for a structural steel beam from its span, as a first guess before choosing and checking a real section. This is a rule-of-thumb starting point only.

Rule of thumb — not a code check; professional review required.Span-to-depth ratios are industry heuristics with no single authoritative published value, and they are unverified against any code calculation. NBCC / CSA S16 impose deflectionlimits (e.g. L/360), not a depth ratio. Use this as a starting point only — every member must be sized and checked properly by a qualified structural engineer.
Ratios used (depth = span ÷ ratio): simply supported ~span/20 (span/15 to span/25); cantilever ~span/8 (span/6 to span/10); continuous / fixed ~span/24 (span/20 to span/28). Deeper beams are stiffer (less deflection); shallower beams save headroom but need checking for deflection.
Beam
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 ca.cad-steel.com accepts no responsibility for its use in any final design.