Steel section data and calculator methodology

Published by Krystian Welcel. Last checked: 10 October 2026. This is a record of our inputs and model, not a structural design certificate.

One section dataset

Source: British Steel, Universal Beams datasheet, 21 July 2026, pages 1 and 3. Transcribed 10 October 2026. Values describe the listed modern UB sections, not unidentified historic RSJs. The calculators and this table share the same data.

The last number in a section designation is nominal mass. For example, 203×133×25 has a listed mass of 25.1 kg/m. Its Iₓ is 2340 cm⁴; 2896 cm⁴ belongs to 203×133×30. We corrected earlier conflicting values. Check the exact supplier designation before ordering.

Load, size, span and deflection tools

The model assumes a straight, prismatic, simply supported beam under a full-span uniformly distributed service load, bending about its major axis. Span L is the distance between idealised support centres. Clear opening width is not necessarily this span.

• Total line load w = (dead area load + imposed area load) × tributary width + beam self-weight.
• Beam self-weight = mass per metre × 9.81 / 1000, in kN/m.
• Each support reaction R = wL / 2; maximum moment M = wL² / 8, using kN/m and metres.
• Elastic section modulus W = 2I / D, using I in mm⁴ and actual depth D in mm.
• Elastic stress = M / W, with M converted from kNm to Nmm by multiplying by 1,000,000.
• Mid-span deflection δ = 5wL⁴ / (384EI), with L in mm and I in mm⁴. 1 kN/m = 1 N/mm; 1 cm⁴ = 10,000 mm⁴.

We use E = 210,000 N/mm², as listed in SteelConstruction.info's material properties guidance. The uniform-load deflection expression is documented in SCI P183, Design of Semi-Continuous Braced Frames.

The standalone deflection calculator takes a total line load including self-weight. The other three tools add self-weight automatically. The selected L/ratio target is a user assumption, not a universal legal limit. A result within that target does not establish strength, stability or suitability.

Reproducible example

For a 203×133×25 UB, a 4 m support-centre span and a total service load of 12 kN/m including self-weight, the model gives 24 kNm moment, 24 kN reaction at each support and approximately 8.14 mm deflection. L/360 is 11.11 mm. This comparison does not prove that the beam is safe.

Checks this model does not perform

There is no verification of load combinations, resistance, yielding, lateral-torsional buckling, shear, web bearing, connections, masonry, padstones, vibration, fire resistance or temporary works. It does not model point loads, cantilevers, continuity, composite action or plastic behaviour. An elastic stress output outside the elastic range is not a valid prediction of actual behaviour.

Other tools

Weight is tabulated mass × ordered length × quantity; it excludes plates, welds and finishes. Bearing length adds the two entered end bearings to the clear opening and does not design those bearings. The cost tool totals user-entered quotes in GBP or PLN; it does not claim live supplier prices or calculate import charges.

Corrections and review

Manufacturer data and automated arithmetic tests improve traceability, but do not constitute an independent engineering review. Send corrections with a source and the affected URL using our contact details. For work in England, consult Approved Document A; other jurisdictions have their own requirements. All structural work must be designed by a chartered structural engineer and receive the applicable Building Control approval.