IPE 300 vs UB 305×165×40
IPE 300 is an IPE section from the European (Continental) range; UB 305×165×40 is the closest equivalent in the UK Blue Book (SCI P363). They are close to interchangeable in bending: 628 cm³ against 623 cm³ of plastic modulus, a difference of 0.8%. UB 305×165×40 is the lighter of the two at 40.3 kg/m against 42.2 kg/m, a saving of 4.7% on steel weight. Both are about 302 mm deep, so either fits the same construction zone.
| Property | IPE 300 IPE | UB 305×165×40 UB | Difference |
|---|---|---|---|
| Mass | 42.2 kg/m | 40.3 kg/m | +4.7% |
| Depth | 300 mm | 303.4 mm | -1.1% |
| Width | 150 mm | 165 mm | -9.1% |
| Web thickness | 7.1 mm | 6 mm | +18.3% |
| Flange thickness | 10.7 mm | 10.2 mm | +4.9% |
| Area | 53.8 cm² | 51.3 cm² | +4.9% |
| Second moment, major (Iy) | 8,360 cm⁴ | 8,500 cm⁴ | -1.6% |
| Plastic modulus, major (Wpl,y) | 628 cm³ | 623 cm³ | +0.8% |
| Elastic modulus, major (Wel,y) | 557 cm³ | 560 cm³ | -0.5% |
| Second moment, minor (Iz) | 604 cm⁴ | 764 cm⁴ | -20.9% |
| Plastic modulus, minor (Wpl,z) | 125 cm³ | 142 cm³ | -12.0% |
| Radius of gyration, minor (iz) | 3.35 cm | 3.86 cm | -13.2% |
| Torsion constant (It) | 19.9 cm⁴ | 14.7 cm⁴ | +35.4% |
IPE 300 to EN 10365 · Continental Steel; UB 305×165×40 to BS EN 10365:2017. Difference is expressed relative to UB 305×165×40.
How to choose between them
On stiffness, UB 305×165×40 has the larger second moment of area: 8,500 cm⁴ against 8,360 cm⁴, a difference of 1.6%. 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, UB 305×165×40 is the more efficient section: 15.5 against 14.9 cm³ per kg/m, 3.7% 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: UB 305×165×40 has 142 cm³ of minor-axis plastic modulus against 125 cm³, 12.0% 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. IPE sections are specified to EN 10365 · Continental Steel and UB to BS EN 10365:2017; 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 4.7% weight.
In short, IPE 300 is the stronger section and UB 305×165×40 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.