UB 203×133×30 vs H-200x150x6x9-30.6
UB 203×133×30 is an UB section from the UK Blue Book (SCI P363); H-200x150x6x9-30.6 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 314 cm³ against 309 cm³ of plastic modulus, a difference of 1.6%. They weigh essentially the same, 30 kg/m and 30.6 kg/m. UB 203×133×30 is deeper, 206.8 mm against 194 mm, which matters where the floor zone is tight.
| Property | UB 203×133×30 UB | H-200x150x6x9-30.6 MB & MC | Difference |
|---|---|---|---|
| Mass | 30 kg/m | 30.6 kg/m | -2.0% |
| Depth | 206.8 mm | 194 mm | +6.6% |
| Width | 133.9 mm | 150 mm | -10.7% |
| Web thickness | 6.4 mm | 6 mm | +6.7% |
| Flange thickness | 9.6 mm | 9 mm | +6.7% |
| Area | 38.2 cm² | 39 cm² | -2.1% |
| Second moment, major (Iy) | 2,900 cm⁴ | 2,690 cm⁴ | +7.8% |
| Plastic modulus, major (Wpl,y) | 314 cm³ | 309 cm³ | +1.6% |
| Elastic modulus, major (Wel,y) | 280 cm³ | 277 cm³ | +1.1% |
| Second moment, minor (Iz) | 385 cm⁴ | 507 cm⁴ | -24.1% |
| Plastic modulus, minor (Wpl,z) | 88.2 cm³ | 104 cm³ | -15.2% |
| Radius of gyration, minor (iz) | 3.17 cm | 3.61 cm | -12.2% |
| Torsion constant (It) | 10.3 cm⁴ | 10.9 cm⁴ | -5.5% |
UB 203×133×30 to BS EN 10365:2017; H-200x150x6x9-30.6 to Continental Steel. Difference is expressed relative to H-200x150x6x9-30.6.
How to choose between them
On stiffness, UB 203×133×30 has the larger second moment of area: 2,900 cm⁴ against 2,690 cm⁴, a difference of 7.8%. This matters more often than the strength comparison, because on normal floor spans deflection rather than bending capacity sets the beam size - so if the two are close on modulus but apart on inertia, the stiffer one is usually the better answer even when it is not the stronger one.
Measured as bending capacity per kilogram of steel, UB 203×133×30 is the more efficient section: 10.5 against 10.1 cm³ per kg/m, 3.7% better. Over a floor of repeated beams that difference is real tonnage, though it is often outweighed by whichever section the fabricator can actually source.
The two diverge much more about the minor axis: H-200x150x6x9-30.6 has 104 cm³ of minor-axis plastic modulus against 88.2 cm³, 15.2% more. If the member sees any minor-axis bending, or if it is unrestrained over a long length and lateral-torsional buckling governs, that gap decides the comparison even though the major-axis numbers looked equivalent.
These come from different catalogues, so treat the swap as a design change rather than a like-for-like substitution. UB sections are specified to BS EN 10365:2017 and MB & MC to Continental Steel; the steel grades, tolerances and available lengths differ, connection details and bolt gauges are set out differently, and the two are rarely both stocked in the same market. Check availability before changing a section on a drawing to save a marginal amount of weight.
In short, these two are genuine equivalents. Pick whichever your supplier stocks and the rest of the frame already uses.