W 12X45 vs S 12X50
W 12X45 is an W section from the American AISC Shapes Database; S 12X50 is the closest equivalent in the American AISC Shapes Database. W 12X45 carries more bending: 1052 cm³ of plastic modulus against 997.97 cm³, 5.4% more. W 12X45 is the lighter of the two at 67 kg/m against 74.4 kg/m, a saving of 9.9% on steel weight. Both are about 306 mm deep, so either fits the same construction zone.
| Property | W 12X45 W | S 12X50 S | Difference |
|---|---|---|---|
| Mass | 67 kg/m | 74.4 kg/m | -9.9% |
| Depth | 307.3 mm | 304.8 mm | +0.8% |
| Width | 204.5 mm | 139.2 mm | +46.9% |
| Web thickness | 8.5 mm | 17.4 mm | -51.1% |
| Flange thickness | 14.6 mm | 16.7 mm | -12.6% |
| Area | 84.5 cm² | 94.8 cm² | -10.9% |
| Second moment, major (Iy) | 14,485 cm⁴ | 12,612 cm⁴ | +14.9% |
| Plastic modulus, major (Wpl,y) | 1,052 cm³ | 997.97 cm³ | +5.4% |
| Elastic modulus, major (Wel,y) | 945.53 cm³ | 829.19 cm³ | +14.0% |
| Second moment, minor (Iz) | 2,081 cm⁴ | 649.3 cm⁴ | +220.5% |
| Plastic modulus, minor (Wpl,z) | 311.35 cm³ | 168.79 cm³ | +84.5% |
| Radius of gyration, minor (iz) | 4.95 cm | 2.62 cm | +88.9% |
| Torsion constant (It) | 52.45 cm⁴ | 115.3 cm⁴ | -54.5% |
W 12X45 to AISC Shapes Database v16.0; S 12X50 to AISC Shapes Database v16.0. Difference is expressed relative to S 12X50.
How to choose between them
On stiffness, W 12X45 has the larger second moment of area: 14,485 cm⁴ against 12,612 cm⁴, a difference of 14.9%. 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 12X45 is the more efficient section: 15.7 against 13.4 cm³ per kg/m, 17.1% 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: W 12X45 has 311.35 cm³ of minor-axis plastic modulus against 168.79 cm³, 84.5% 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.
In short, W 12X45 is the stronger section and W 12X45 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.