UB 305×165×54 vs H-300x200x8x12-55.8
UB 305×165×54 is an UB section from the UK Blue Book (SCI P363); H-300x200x8x12-55.8 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 846 cm³ against 842 cm³ of plastic modulus, a difference of 0.5%. UB 305×165×54 is the lighter of the two at 54 kg/m against 55.8 kg/m, a saving of 3.2% on steel weight. UB 305×165×54 is deeper, 310.4 mm against 294 mm, which matters where the floor zone is tight.
| Property | UB 305×165×54 UB | H-300x200x8x12-55.8 MB & MC | Difference |
|---|---|---|---|
| Mass | 54 kg/m | 55.8 kg/m | -3.2% |
| Depth | 310.4 mm | 294 mm | +5.6% |
| Width | 166.9 mm | 200 mm | -16.5% |
| Web thickness | 7.9 mm | 8 mm | -1.2% |
| Flange thickness | 13.7 mm | 12 mm | +14.2% |
| Area | 68.8 cm² | 71.1 cm² | -3.2% |
| Second moment, major (Iy) | 11,700 cm⁴ | 11,110 cm⁴ | +5.3% |
| Plastic modulus, major (Wpl,y) | 846 cm³ | 842 cm³ | +0.5% |
| Elastic modulus, major (Wel,y) | 754 cm³ | 756 cm³ | -0.3% |
| Second moment, minor (Iz) | 1,060 cm⁴ | 1,602 cm⁴ | -33.8% |
| Plastic modulus, minor (Wpl,z) | 196 cm³ | 245 cm³ | -20.0% |
| Radius of gyration, minor (iz) | 3.93 cm | 4.75 cm | -17.3% |
| Torsion constant (It) | 34.8 cm⁴ | 31.4 cm⁴ | +10.8% |
UB 305×165×54 to BS EN 10365:2017; H-300x200x8x12-55.8 to Continental Steel. Difference is expressed relative to H-300x200x8x12-55.8.
How to choose between them
On stiffness, UB 305×165×54 has the larger second moment of area: 11,700 cm⁴ against 11,110 cm⁴, a difference of 5.3%. 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 305×165×54 is the more efficient section: 15.7 against 15.1 cm³ per kg/m, 3.8% 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-300x200x8x12-55.8 has 245 cm³ of minor-axis plastic modulus against 196 cm³, 20.0% 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 3.2% weight.
In short, UB 305×165×54 is the stronger section and UB 305×165×54 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.