UB 305×127×48 vs H-300x150x7.5x12
UB 305×127×48 is an UB section from the UK Blue Book (SCI P363); H-300x150x7.5x12 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 711 cm³ against 702 cm³ of plastic modulus, a difference of 1.3%. H-300x150x7.5x12 is the lighter of the two at 46.2 kg/m against 48.1 kg/m, a saving of 4.1% on steel weight. Both are about 309 mm deep, so either fits the same construction zone.
| Property | UB 305×127×48 UB | H-300x150x7.5x12 MB & MC | Difference |
|---|---|---|---|
| Mass | 48.1 kg/m | 46.2 kg/m | +4.1% |
| Depth | 311 mm | 306 mm | +1.6% |
| Width | 125.3 mm | 151 mm | -17.0% |
| Web thickness | 9 mm | 7.5 mm | +20.0% |
| Flange thickness | 14 mm | 12 mm | +16.7% |
| Area | 61.3 cm² | 58.8 cm² | +4.3% |
| Second moment, major (Iy) | 9,570 cm⁴ | 9,514 cm⁴ | +0.6% |
| Plastic modulus, major (Wpl,y) | 711 cm³ | 702 cm³ | +1.3% |
| Elastic modulus, major (Wel,y) | 616 cm³ | 622 cm³ | -1.0% |
| Second moment, minor (Iz) | 461 cm⁴ | 691 cm⁴ | -33.3% |
| Plastic modulus, minor (Wpl,z) | 116 cm³ | 142 cm³ | -18.3% |
| Radius of gyration, minor (iz) | 2.74 cm | 3.43 cm | -20.1% |
| Torsion constant (It) | 31.8 cm⁴ | 24.9 cm⁴ | +27.7% |
UB 305×127×48 to BS EN 10365:2017; H-300x150x7.5x12 to Continental Steel. Difference is expressed relative to H-300x150x7.5x12.
How to choose between them
On stiffness, UB 305×127×48 has the larger second moment of area: 9,570 cm⁴ against 9,514 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 of steel, H-300x150x7.5x12 is the more efficient section: 15.2 against 14.8 cm³ per kg/m, 2.7% 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-300x150x7.5x12 has 142 cm³ of minor-axis plastic modulus against 116 cm³, 18.3% 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 4.1% weight.
In short, UB 305×127×48 is the stronger section and H-300x150x7.5x12 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.