The 203 x 203 UC46 universal column is the entry section in the 203 x 203 range and the point at which columns move from domestic to genuinely structural. At 46.1kg per metre with an 11mm flange, it carries roughly double the axial load of a 152 x 152 UC23 — and because it is a true 203mm square, its weak-axis radius of gyration jumps to 5.1cm against 3.8cm for the largest 152 section. 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 column 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 203 x 203 changes the calculation
Stepping from 152 x 152 UC37 to UC46 adds only 9kg per metre, but the section is 50mm wider and deeper. Because buckling capacity depends on the square of the radius of gyration against effective length, that geometry matters far more than the extra steel.
The weak-axis radius of gyration rises from 3.8cm to 5.1cm — a 34% increase. Over a 4m unrestrained height that translates into a step-change in capacity, not an incremental one. It is the reason a 203 x 203 will often solve a column that three successive 152 x 152 sections could not.
The trade-off is footprint. A 203mm square column will not disappear inside a standard stud wall, so it usually has to be boxed out or accepted as a visible element. Where that is a problem, check whether a heavier 152 section clears the design first. See UB vs UC, what UK builders actually specify, and the UK steel beam size chart for every size with weights.
Where the UC46 is typically used
Carrying beams over two or more storeys, in steel-framed extensions and garden rooms, supporting mezzanine floors, and as the main posts in car ports and open-sided structures. It also appears in larger load-bearing wall removals where the opening runs the full width of a property and the column takes load from above as well as the beam.
Available finishes
Mill finish is the column exactly as it leaves the rolling mill: bare structural steel carrying the usual blue-grey mill scale. It suits any job where the column will be encased, boxed in, fire-protected or painted on site — see our guide to boxing in steelwork, or whether structural steel needs painting at all.
Red oxide primer is a factory-applied anti-corrosive coating, shot blasted and painted, that protects the steel while it stands on site before the building is closed in. At this size the column is often erected as part of a frame and left exposed for weeks, which makes primer worth taking. It is a primer rather than a topcoat — designed to be overpainted, and not a substitute for intumescent fire protection or galvanising outdoors. More in what red oxide primer actually means.
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 2.7m requirement is charged as 3m; where you order more than one cut in the same finish, the total is rounded once rather than cut by cut, which matters when a frame needs four or six posts.
Cut tolerance is ±3mm on length. Tell us if your head detail is critical, and confirm the base plate, padstone and holding-down bolt arrangement with your engineer before ordering. More on what lengths structural steel comes in.
Section dimensions
| Depth of section (h) | 203.2 mm |
| Width of section (b) | 203.6 mm |
| Web thickness (s) | 7.2 mm |
| Flange thickness (t) | 11.0 mm |
| Root radius (r) | 10.0 mm |
| Depth between fillets (d) | 161.2 mm |
| Mass per metre | 46.1 kg/m |
| Cross-sectional area | 58.7 cm² |
| Surface area per metre | 1.189 m²/m |
Section properties
| Second moment of area, y-y (Iy) | 4,565 cm⁴ |
| Second moment of area, z-z (Iz) | 1,548 cm⁴ |
| Elastic modulus, y-y (Wel,y) | 449.3 cm³ |
| Elastic modulus, z-z (Wel,z) | 152.0 cm³ |
| Plastic modulus, y-y (Wpl,y) | 497.1 cm³ |
| Plastic modulus, z-z (Wpl,z) | 230.8 cm³ |
| Radius of gyration, y-y (iy) | 8.8 cm |
| Radius of gyration, z-z (iz) | 5.1 cm |
Nominal dimensions and properties to BS EN 10365. Figures are published for reference only.
Structural engineer notice
Column sizing cannot be taken from a table. Capacity depends on the axial load, the effective length between restraints, the end fixity, any bending applied at the connections, and the base and head details — all of which must be calculated by a qualified structural engineer, and in most cases will form part of your building control submission. Base plates, padstones and holding-down bolts are part of that design. We supply steel to the specification you give us; we do not provide structural design.
Delivery — plan the lift
Cut-to-size steel is 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 46.1kg per metre a 3m post is 138kg and a 5m post is 231kg. Deliveries are kerbside and offloading assistance is required — our vehicles do not carry lifting equipment. At this size we strongly recommend a telehandler or forklift rather than manpower. See how structural steel is delivered, or our delivery & lead times page. Ordering a full frame? Trade discounts are available.
Related sections
- 203 x 203 UC52 steel column — next section up in the same serial size
- 152 x 152 UC37 steel column — smaller footprint where space is tight
- 254 x 254 UC73 steel column — heavy section for the highest loads
- All universal columns (UC)
- All RSJ steel beams & columns