RSJ deflection calculator

Calculate elastic mid-span deflection under a full-span uniform service load using the listed UB second moment of area.

How to use this tool

  1. Select the section and enter its support-centre span.
  2. Enter total uniform service load including beam self-weight. It is not added again.
  3. Set the comparison ratio and calculate. Your engineer must choose a project-specific serviceability limit.

RSJ deflection calculator

Simply supported beam, major-axis bending, uniform service load. This model does not establish a safe load or approve a beam size.

Include beam self-weight in your total input. The ratio is an illustrative target you choose, not a universal Building Regulations limit.

Professional design required. A chartered structural engineer must determine loads, effective span, restraints, suitable section and project-specific limits. Obtain the required Building Control approval before structural work.

Data: British Steel UB datasheet, 21 July 2026. Section values, formulas and limitations.

Questions and limitations

Does a result within the target mean the beam is safe?

No. It compares elastic deflection with your chosen target only. There is no code-compliant strength or stability check, safe load rating or final beam recommendation.

Where do the section properties come from?

The tools share data transcribed from the British Steel Universal Beams datasheet dated 21 July 2026. See the methodology page for values, formulas and sources.

Can I model a point load, cantilever or continuous beam?

No. This model is restricted to a simply supported beam under a full-span uniformly distributed service load. Obtain project-specific calculations from a chartered structural engineer.

Data and editorial responsibility

Published by Krystian Welcel, a software developer. These tools have not received an independent structural engineering review. Read the data sources and calculation method.

Structural work must be designed by a chartered structural engineer and receive the applicable Building Control approval. These educational calculations are not construction specifications.