UB 305×127×42 vs W 12X26
UB 305×127×42 is an UB section from the UK Blue Book (SCI P363); W 12X26 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 614 cm³ against 609.6 cm³ of plastic modulus, a difference of 0.7%. W 12X26 is the lighter of the two at 38.7 kg/m against 41.9 kg/m, a saving of 8.3% on steel weight. Both are about 309 mm deep, so either fits the same construction zone.
| Property | UB 305×127×42 UB | W 12X26 W | Difference |
|---|---|---|---|
| Mass | 41.9 kg/m | 38.7 kg/m | +8.3% |
| Depth | 307.2 mm | 309.9 mm | -0.9% |
| Width | 124.3 mm | 164.8 mm | -24.6% |
| Web thickness | 8 mm | 5.8 mm | +37.9% |
| Flange thickness | 12.1 mm | 9.7 mm | +24.7% |
| Area | 53.4 cm² | 49.4 cm² | +8.1% |
| Second moment, major (Iy) | 8,200 cm⁴ | 8,491 cm⁴ | -3.4% |
| Plastic modulus, major (Wpl,y) | 614 cm³ | 609.6 cm³ | +0.7% |
| Elastic modulus, major (Wel,y) | 534 cm³ | 547.33 cm³ | -2.4% |
| Second moment, minor (Iz) | 389 cm⁴ | 720.1 cm⁴ | -46.0% |
| Plastic modulus, minor (Wpl,z) | 98.4 cm³ | 133.88 cm³ | -26.5% |
| Radius of gyration, minor (iz) | 2.7 cm | 3.84 cm | -29.7% |
| Torsion constant (It) | 21.1 cm⁴ | 12.49 cm⁴ | +68.9% |
UB 305×127×42 to BS EN 10365:2017; W 12X26 to AISC Shapes Database v16.0. Difference is expressed relative to W 12X26.
How to choose between them
On stiffness, W 12X26 has the larger second moment of area: 8,491 cm⁴ against 8,200 cm⁴, a difference of 3.4%. 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, W 12X26 is the more efficient section: 15.8 against 14.7 cm³ per kg/m, 7.0% 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: W 12X26 has 133.88 cm³ of minor-axis plastic modulus against 98.4 cm³, 26.5% 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 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 8.3% weight.
In short, UB 305×127×42 is the stronger section and W 12X26 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.