WT 4X12 vs ST 4X9.2
WT 4X12 is an WT section from the American AISC Shapes Database; ST 4X9.2 is the closest equivalent in the American AISC Shapes Database. ST 4X9.2 carries more bending: 33.921 cm³ of plastic modulus against 32.446 cm³, 4.3% more. ST 4X9.2 is the lighter of the two at 13.7 kg/m against 17.9 kg/m, a saving of 30.7% on steel weight. Both are about 101 mm deep, so either fits the same construction zone.
| Property | WT 4X12 WT | ST 4X9.2 ST | Difference |
|---|---|---|---|
| Mass | 17.9 kg/m | 13.7 kg/m | +30.7% |
| Depth | 100.8 mm | 101.6 mm | -0.8% |
| Width | 165.1 mm | 101.6 mm | +62.5% |
| Web thickness | 6.2 mm | 6.9 mm | -10.1% |
| Flange thickness | 10.2 mm | 10.8 mm | -5.6% |
| Area | 22.8 cm² | 17.4 cm² | +31.0% |
| Second moment, major (Iy) | 146.9 cm⁴ | 145.3 cm⁴ | +1.1% |
| Plastic modulus, major (Wpl,y) | 32.446 cm³ | 33.921 cm³ | -4.3% |
| Elastic modulus, major (Wel,y) | 17.698 cm³ | 18.681 cm³ | -5.3% |
| Second moment, minor (Iz) | 380.4 cm⁴ | 76.59 cm⁴ | +396.7% |
| Plastic modulus, minor (Wpl,z) | 70.137 cm³ | 26.055 cm³ | +169.2% |
| Radius of gyration, minor (iz) | 4.09 cm | 2.1 cm | +94.8% |
| Torsion constant (It) | 7.2 cm⁴ | 6.95 cm⁴ | +3.6% |
WT 4X12 to AISC Shapes Database v16.0; ST 4X9.2 to AISC Shapes Database v16.0. Difference is expressed relative to ST 4X9.2.
How to choose between them
On stiffness, WT 4X12 has the larger second moment of area: 146.9 cm⁴ against 145.3 cm⁴, a difference of 1.1%. 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 4X9.2 is the more efficient section: 2.5 against 1.8 cm³ per kg/m, 26.8% 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 4X12 has 70.137 cm³ of minor-axis plastic modulus against 26.055 cm³, 169.2% 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 4X9.2 is the stronger section and ST 4X9.2 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.