The 254 x 146 UB43 steel beam is the heaviest section in the 254 x 146 range — 259.6mm deep, 147.3mm wide, with a substantial 12.7mm flange and a 7.2mm web. At 43kg per metre it is the point where domestic steelwork starts to need mechanical lifting, and it is specified where a single beam must carry heavy loads over a wide opening without intermediate support. Rolled to S355J0 and supplied cut free to any length from 1m to 12m, 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.
The top of the 254 x 146 range
All three 254 x 146 sections share the same nominal footprint, so they bear and detail alike. The UB43 simply puts more metal where it counts: a 12.7mm flange against the UB37's 10.9mm and the UB31's 8.6mm.
That gives a major-axis second moment of area of 6,550 cm⁴ — 18% above the UB37 and 48% above the UB31 — and a plastic modulus of 566.9 cm³. Minor-axis stiffness reaches 677.3 cm⁴, so the section is markedly more tolerant of long unrestrained spans. If your engineer has run a UB37 and it fails on deflection, this is the section that usually solves it without increasing the structural opening height.
At this weight the beam is typically carrying a full storey. It is a common specification on large load-bearing wall removals and full-width rear extensions. The UK steel beam size chart lists every UB, UC and PFC size with weights.
Mill finish
This section is supplied in mill finish — bare structural steel exactly as it leaves the rolling mill, carrying the usual blue-grey mill scale, handling marks and light surface oxidation that are normal for untreated steel. This is the correct specification where the beam 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, or whether RSJs need painting at all.
Store it dry and ventilated before installation. If the beam will be exposed, visible or used externally, it should be cleaned, prepared and protected with a suitable coating, galvanising or fire-protection system as required by the project specification.
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, 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) | 259.6 mm |
| Width of section (b) | 147.3 mm |
| Web thickness (s) | 7.2 mm |
| Flange thickness (t) | 12.7 mm |
| Root radius (r) | 8.0 mm |
| Depth between fillets (d) | 218.2 mm |
| Mass per metre | 43.0 kg/m |
| Cross-sectional area | 54.8 cm² |
| Surface area per metre | 1.080 m²/m |
Section properties
| Second moment of area, y-y (Iy) | 6,550 cm⁴ |
| Second moment of area, z-z (Iz) | 677.3 cm⁴ |
| Elastic modulus, y-y (Wel,y) | 504.6 cm³ |
| Elastic modulus, z-z (Wel,z) | 91.97 cm³ |
| Plastic modulus, y-y (Wpl,y) | 566.9 cm³ |
| Plastic modulus, z-z (Wpl,z) | 141.1 cm³ |
| Radius of gyration, y-y (iy) | 10.9 cm |
| Radius of gyration, z-z (iz) | 3.5 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 — plan the lift
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.
At 43kg per metre this is a heavy section: a 4m beam is 172kg and a 6m beam is 258kg. Deliveries are kerbside and offloading assistance is required — our vehicles do not carry lifting equipment. For this size we strongly recommend arranging a telehandler, forklift or crane rather than relying on manpower. See how RSJ steel beams are delivered for what to expect on the day, or our delivery & lead times page. Ordering several beams for one project? Trade discounts are available.
Related sections
- 254 x 146 UB37 steel beam — lighter section in the same serial size
- 254 x 146 UB31 steel beam — lightest section in the same serial size
- 254 x 102 UB28 steel beam — narrower alternative at similar depth
- All RSJ steel beams & columns
- Universal beams (UB)