UB 305×127×42 vs IPE 300
UB 305×127×42 is an UB section from the UK Blue Book (SCI P363); IPE 300 is the closest equivalent in the European (Continental) range. IPE 300 carries more bending: 628 cm³ of plastic modulus against 614 cm³, 2.2% more. They weigh essentially the same, 41.9 kg/m and 42.2 kg/m. UB 305×127×42 is deeper, 307.2 mm against 300 mm, which matters where the floor zone is tight.
| Property | UB 305×127×42 UB | IPE 300 IPE | Difference |
|---|---|---|---|
| Mass | 41.9 kg/m | 42.2 kg/m | -0.7% |
| Depth | 307.2 mm | 300 mm | +2.4% |
| Width | 124.3 mm | 150 mm | -17.1% |
| Web thickness | 8 mm | 7.1 mm | +12.7% |
| Flange thickness | 12.1 mm | 10.7 mm | +13.1% |
| Area | 53.4 cm² | 53.8 cm² | -0.7% |
| Second moment, major (Iy) | 8,200 cm⁴ | 8,360 cm⁴ | -1.9% |
| Plastic modulus, major (Wpl,y) | 614 cm³ | 628 cm³ | -2.2% |
| Elastic modulus, major (Wel,y) | 534 cm³ | 557 cm³ | -4.1% |
| Second moment, minor (Iz) | 389 cm⁴ | 604 cm⁴ | -35.6% |
| Plastic modulus, minor (Wpl,z) | 98.4 cm³ | 125 cm³ | -21.3% |
| Radius of gyration, minor (iz) | 2.7 cm | 3.35 cm | -19.4% |
| Torsion constant (It) | 21.1 cm⁴ | 19.9 cm⁴ | +6.0% |
UB 305×127×42 to BS EN 10365:2017; IPE 300 to EN 10365 · Continental Steel. Difference is expressed relative to IPE 300.
How to choose between them
On stiffness, IPE 300 has the larger second moment of area: 8,360 cm⁴ against 8,200 cm⁴, a difference of 1.9%. 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 (14.7 against 14.9 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: IPE 300 has 125 cm³ of minor-axis plastic modulus against 98.4 cm³, 21.3% 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 IPE to EN 10365 · 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, IPE 300 is the stronger section and UB 305×127×42 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.