WT 6X43.5 vs ST 6X25
WT 6X43.5 is an WT section from the American AISC Shapes Database; ST 6X25 is the closest equivalent in the American AISC Shapes Database. ST 6X25 carries more bending: 180.26 cm³ of plastic modulus against 175.34 cm³, 2.7% more. ST 6X25 is the lighter of the two at 37.2 kg/m against 64.7 kg/m, a saving of 73.9% on steel weight. WT 6X43.5 is deeper, 159.3 mm against 152.4 mm, which matters where the floor zone is tight.
| Property | WT 6X43.5 WT | ST 6X25 ST | Difference |
|---|---|---|---|
| Mass | 64.7 kg/m | 37.2 kg/m | +73.9% |
| Depth | 159.3 mm | 152.4 mm | +4.5% |
| Width | 307.3 mm | 139.2 mm | +120.8% |
| Web thickness | 13.1 mm | 17.4 mm | -24.7% |
| Flange thickness | 20.6 mm | 16.7 mm | +23.4% |
| Area | 82.6 cm² | 47.3 cm² | +74.6% |
| Second moment, major (Iy) | 1,203 cm⁴ | 1,045 cm⁴ | +15.1% |
| Plastic modulus, major (Wpl,y) | 175.34 cm³ | 180.26 cm³ | -2.7% |
| Elastic modulus, major (Wel,y) | 91.768 cm³ | 98.978 cm³ | -7.3% |
| Second moment, minor (Iz) | 4,995 cm⁴ | 324.2 cm⁴ | +1440.7% |
| Plastic modulus, minor (Wpl,z) | 494.89 cm³ | 84.557 cm³ | +485.3% |
| Radius of gyration, minor (iz) | 7.8 cm | 2.62 cm | +197.7% |
| Torsion constant (It) | 105.7 cm⁴ | 56.61 cm⁴ | +86.7% |
WT 6X43.5 to AISC Shapes Database v16.0; ST 6X25 to AISC Shapes Database v16.0. Difference is expressed relative to ST 6X25.
How to choose between them
On stiffness, WT 6X43.5 has the larger second moment of area: 1,203 cm⁴ against 1,045 cm⁴, a difference of 15.1%. 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, ST 6X25 is the more efficient section: 4.8 against 2.7 cm³ per kg/m, 44.1% 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: WT 6X43.5 has 494.89 cm³ of minor-axis plastic modulus against 84.557 cm³, 485.3% 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.
In short, ST 6X25 is the stronger section and ST 6X25 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.