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There is no fixed maximum span for a steel beam. The answer depends on the section, the load, and which limit governs. Because those three interact, the span is found by iteration rather than read off a table.

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Why a span table does not settle it

A span figure only means something alongside the section size, the load, and the deflection limit it assumes. Change any one of those and the answer moves. Two beams of the same section can have very different usable spans under different loads.

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The iteration method

Use the beam calculator and work in this order.
  1. Fix the section. Choose the section you expect to use.
  2. Fix the load. Enter the loads the member actually carries.
  3. Raise the beam length step by step.
  4. Stop at the first limit reached. That is either deflection reaching your serviceability limit, or moment demand reaching the capacity of the section.
Whichever limit arrives first governs the span. On longer, lightly loaded members, deflection usually governs. On short, heavily loaded members, strength is more often the constraint.

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Common deflection limits

Two limits are applied most often:
  • L/360 for floor members
  • L/240 for roof members
Treat these as the common cases, not as a rule for your project. The governing value comes from your project requirements, and from the standard and the client specification that apply to the job.

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Strength is a separate check

The beam calculator returns analysis output such as moment and shear demand. Comparing that demand against a section capacity is a design check. It runs against the governing standard, for example AISC, NDS, ACI 318, or AS 4100. Run that check before you rely on a span. Lateral-torsional buckling deserves particular attention on long steel spans. A section that satisfies deflection and moment demand may still fail once restraint conditions are taken into account.

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Practical notes

  • Check the serviceability load case, not the factored case, against the deflection limit.
  • Consider whether the deflection limit applies to total load or to live load only.
  • Confirm the restraint assumptions match what will be built.
The calculator does the arithmetic. Selecting limits, load cases, and restraint assumptions remains an engineering judgment.