UB 305×127×37 vs H-300x150x6.5x9
UB 305×127×37 is an UB section from the UK Blue Book (SCI P363); H-300x150x6.5x9 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 539 cm³ against 542 cm³ of plastic modulus, a difference of 0.6%. They weigh essentially the same, 37 kg/m and 36.7 kg/m. Both are about 302 mm deep, so either fits the same construction zone.
| Property | UB 305×127×37 UB | H-300x150x6.5x9 MB & MC | Difference |
|---|---|---|---|
| Mass | 37 kg/m | 36.7 kg/m | +0.8% |
| Depth | 304.4 mm | 300 mm | +1.5% |
| Width | 123.4 mm | 150 mm | -17.7% |
| Web thickness | 7.1 mm | 6.5 mm | +9.2% |
| Flange thickness | 10.7 mm | 9 mm | +18.9% |
| Area | 47.1 cm² | 46.8 cm² | +0.6% |
| Second moment, major (Iy) | 7,170 cm⁴ | 7,210 cm⁴ | -0.6% |
| Plastic modulus, major (Wpl,y) | 539 cm³ | 542 cm³ | -0.6% |
| Elastic modulus, major (Wel,y) | 471 cm³ | 481 cm³ | -2.1% |
| Second moment, minor (Iz) | 336 cm⁴ | 508 cm⁴ | -33.9% |
| Plastic modulus, minor (Wpl,z) | 85.4 cm³ | 105 cm³ | -18.7% |
| Radius of gyration, minor (iz) | 2.67 cm | 3.29 cm | -18.8% |
| Torsion constant (It) | 14.8 cm⁴ | 12.4 cm⁴ | +19.4% |
UB 305×127×37 to BS EN 10365:2017; H-300x150x6.5x9 to Continental Steel. Difference is expressed relative to H-300x150x6.5x9.
How to choose between them
On stiffness, H-300x150x6.5x9 has the larger second moment of area: 7,210 cm⁴ against 7,170 cm⁴, a difference of 0.6%. 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, the two are equally efficient (14.6 against 14.8 cm³ per kg/m), so on a pure steel-tonnage basis there is nothing to choose between them. The decision comes down to availability, connection detailing and what the rest of the frame uses.
The two diverge much more about the minor axis: H-300x150x6.5x9 has 105 cm³ of minor-axis plastic modulus against 85.4 cm³, 18.7% 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.