UB 305×102×25 vs W 12X16
UB 305×102×25 is an UB section from the UK Blue Book (SCI P363); W 12X16 is the closest equivalent in the American AISC Shapes Database. UB 305×102×25 carries more bending: 342 cm³ of plastic modulus against 329.38 cm³, 3.8% more. W 12X16 is the lighter of the two at 23.8 kg/m against 24.8 kg/m, a saving of 4.2% on steel weight. Both are about 305 mm deep, so either fits the same construction zone.
| Property | UB 305×102×25 UB | W 12X16 W | Difference |
|---|---|---|---|
| Mass | 24.8 kg/m | 23.8 kg/m | +4.2% |
| Depth | 305.1 mm | 304.8 mm | +0.1% |
| Width | 101.6 mm | 101.3 mm | +0.3% |
| Web thickness | 5.8 mm | 5.6 mm | +3.6% |
| Flange thickness | 7 mm | 6.7 mm | +4.5% |
| Area | 31.6 cm² | 30.4 cm² | +3.9% |
| Second moment, major (Iy) | 4,460 cm⁴ | 4,287 cm⁴ | +4.0% |
| Plastic modulus, major (Wpl,y) | 342 cm³ | 329.38 cm³ | +3.8% |
| Elastic modulus, major (Wel,y) | 292 cm³ | 280.22 cm³ | +4.2% |
| Second moment, minor (Iz) | 123 cm⁴ | 117.4 cm⁴ | +4.8% |
| Plastic modulus, minor (Wpl,z) | 38.8 cm³ | 37.035 cm³ | +4.8% |
| Radius of gyration, minor (iz) | 1.97 cm | 1.96 cm | +0.5% |
| Torsion constant (It) | 4.77 cm⁴ | 4.29 cm⁴ | +11.2% |
UB 305×102×25 to BS EN 10365:2017; W 12X16 to AISC Shapes Database v16.0. Difference is expressed relative to W 12X16.
How to choose between them
On stiffness, UB 305×102×25 has the larger second moment of area: 4,460 cm⁴ against 4,287 cm⁴, a difference of 4.0%. 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 (13.8 against 13.8 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.
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 W to AISC Shapes Database v16.0; 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 4.2% weight.
In short, UB 305×102×25 is the stronger section and W 12X16 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.