UB 305×127×42 vs H-300x150x6.5x11
UB 305×127×42 is an UB section from the UK Blue Book (SCI P363); H-300x150x6.5x11 is the closest equivalent in the European (Continental) range. H-300x150x6.5x11 carries more bending: 633 cm³ of plastic modulus against 614 cm³, 3.0% more. They weigh essentially the same, 41.9 kg/m and 41.4 kg/m. Both are about 306 mm deep, so either fits the same construction zone.
| Property | UB 305×127×42 UB | H-300x150x6.5x11 MB & MC | Difference |
|---|---|---|---|
| Mass | 41.9 kg/m | 41.4 kg/m | +1.2% |
| Depth | 307.2 mm | 304 mm | +1.1% |
| Width | 124.3 mm | 150 mm | -17.1% |
| Web thickness | 8 mm | 6.5 mm | +23.1% |
| Flange thickness | 12.1 mm | 11 mm | +10.0% |
| Area | 53.4 cm² | 52.8 cm² | +1.1% |
| Second moment, major (Iy) | 8,200 cm⁴ | 8,578 cm⁴ | -4.4% |
| Plastic modulus, major (Wpl,y) | 614 cm³ | 633 cm³ | -3.0% |
| Elastic modulus, major (Wel,y) | 534 cm³ | 564 cm³ | -5.3% |
| Second moment, minor (Iz) | 389 cm⁴ | 620 cm⁴ | -37.3% |
| Plastic modulus, minor (Wpl,z) | 98.4 cm³ | 128 cm³ | -23.1% |
| Radius of gyration, minor (iz) | 2.7 cm | 3.43 cm | -21.3% |
| Torsion constant (It) | 21.1 cm⁴ | 18.8 cm⁴ | +12.2% |
UB 305×127×42 to BS EN 10365:2017; H-300x150x6.5x11 to Continental Steel. Difference is expressed relative to H-300x150x6.5x11.
How to choose between them
On stiffness, H-300x150x6.5x11 has the larger second moment of area: 8,578 cm⁴ against 8,200 cm⁴, a difference of 4.4%. 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, H-300x150x6.5x11 is the more efficient section: 15.3 against 14.7 cm³ per kg/m, 4.2% 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-300x150x6.5x11 has 128 cm³ of minor-axis plastic modulus against 98.4 cm³, 23.1% 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, H-300x150x6.5x11 is the stronger section and H-300x150x6.5x11 is the lighter one; where those are the same section, it is the clear choice, and where they are not, decide on whether your design is governed by capacity or by tonnage.