The 254 x 146 UB31 steel beam is the entry section in the 254 x 146 serial size and one of the most useful beams in UK domestic construction. At 146.1mm wide it carries a substantially broader flange than the 254 x 102 range for only a little more weight — which buys lateral stability, easier bearing detail and a more forgiving beam on site. Rolled to S355J0 and supplied cut free to any length from 1m to 12m in mill finish or red oxide primer, with free UK mainland delivery included in the price.
Steel grade — S355J0 to BS EN 10025-2
This beam is rolled in S355J0: a 355 N/mm² minimum yield structural steel with impact toughness certified at 0°C. S355 is the grade UK structural engineers design to by default, carrying roughly 29% more yield strength than the older S275 material some merchants still stock. If your engineer has calculated to S275, an S355 section of the same size will always satisfy that design — but never substitute in the opposite direction without going back to them first.
For a fuller comparison see our guide to S275 vs S355 steel, or the steel grades & standards reference for the full specification we supply against.
Why the wider flange matters
Compared with the 254 x 102 UB28, the UB31 is actually 9mm shallower (251.4mm against 260.4mm) yet stiffer about the major axis — 4,420 cm⁴ against 4,012 cm⁴. The real difference is minor-axis stiffness: 447.5 cm⁴ against 178.5 cm⁴, two and a half times as much.
That matters because most domestic beams are not fully restrained along their length. A narrow section relies on the builder providing lateral restraint; a 146mm flange is far more tolerant of imperfect restraint and gives a wider seating for joist hangers and masonry above. Where an engineer specifies 254 x 146 rather than 254 x 102, buckling rather than bending is usually the reason.
This size is a common specification when removing a load-bearing wall or opening up a through-lounge. If you are still narrowing down the section, the UK steel beam size chart lists every UB, UC and PFC size with weights.
Available finishes
Mill finish is the beam exactly as it leaves the rolling mill: bare structural steel carrying the usual blue-grey mill scale. It is the right choice where the RSJ will be encased in plasterboard, boxed in, fire-protected or painted on site by your own decorator — see our guide to boxing in a steel beam.
Red oxide primer is a factory-applied anti-corrosive coating that protects the beam while it sits on site, in transit, or in an unheated shell before the roof and windows go in. It is a primer, not a topcoat — designed to be overpainted, and not a substitute for intumescent fire protection or galvanising in an exposed external location. We cover this in detail in what red oxide primer actually means, and whether RSJs need painting at all.
Cut to size — free, to the millimetre
Tell us the length you need and we cut it. There is no charge for cutting and no minimum order beyond a single metre. Enter your dimensions in the calculator above — you can specify several cut lengths on one order and the tool works out what you need. Steel is supplied and billed in whole metres, so a 4.2m requirement is charged as 5m; where you order more than one cut in the same finish, the total is rounded once rather than cut by cut, which keeps the cost down on multi-beam jobs.
Cut tolerance is ±3mm on length. If your opening is tight, allow the usual bearing at each end and confirm the padstone detail with your engineer before ordering. More on what lengths RSJ beams come in.
Section dimensions
| Depth of section (h) | 251.4 mm |
| Width of section (b) | 146.1 mm |
| Web thickness (s) | 6.0 mm |
| Flange thickness (t) | 8.6 mm |
| Root radius (r) | 8.0 mm |
| Depth between fillets (d) | 218.2 mm |
| Mass per metre | 31.1 kg/m |
| Cross-sectional area | 39.7 cm² |
| Surface area per metre | 1.061 m²/m |
Section properties
| Second moment of area, y-y (Iy) | 4,420 cm⁴ |
| Second moment of area, z-z (Iz) | 447.5 cm⁴ |
| Elastic modulus, y-y (Wel,y) | 351.6 cm³ |
| Elastic modulus, z-z (Wel,z) | 61.26 cm³ |
| Plastic modulus, y-y (Wpl,y) | 393.6 cm³ |
| Plastic modulus, z-z (Wpl,z) | 94.15 cm³ |
| Radius of gyration, y-y (iy) | 10.5 cm |
| Radius of gyration, z-z (iz) | 3.3 cm |
Nominal dimensions and properties to BS EN 10365. Figures are published for reference only.
Structural engineer notice
Beam sizing is not something to work out from a table. The correct section for your opening depends on span, the loads carried above, bearing conditions, lateral restraint and the padstone detail — all of which must be calculated by a qualified structural engineer, and in most cases will form part of your building control submission. We supply steel to the specification you give us; we do not provide structural design.
Delivery
Cut-to-size beams are dispatched on a 5–10 working day lead time, with free delivery to UK mainland addresses included in the price — no carriage is added at checkout. A 254 x 146 UB31 weighs 31.1kg per metre, so a 5m beam is 156kg. Deliveries are kerbside and offloading assistance is required — our vehicles do not carry lifting equipment, so please have suitable labour or plant available.
See how RSJ steel beams are delivered for what to expect on the day, or our delivery & lead times page. Ordering several beams for a single project? Trade discounts are available.
Related sections
- 254 x 146 UB37 steel beam — heavier section in the same serial size
- 254 x 102 UB28 steel beam — narrower alternative at similar depth
- 203 x 133 UB30 steel beam — shallower option for shorter spans
- All RSJ steel beams & columns
- Universal beams (UB)