W 21X166 vs HE 500 M
W 21X166 is an W section from the American AISC Shapes Database; HE 500 M is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 7079.2 cm³ against 7090 cm³ of plastic modulus, a difference of 0.2%. W 21X166 is the lighter of the two at 247 kg/m against 270 kg/m, a saving of 8.5% on steel weight. W 21X166 is deeper, 571.5 mm against 524 mm, which matters where the floor zone is tight.
| Property | W 21X166 W | HE 500 M HE | Difference |
|---|---|---|---|
| Mass | 247 kg/m | 270 kg/m | -8.5% |
| Depth | 571.5 mm | 524 mm | +9.1% |
| Width | 315 mm | 306 mm | +2.9% |
| Web thickness | 19 mm | 21 mm | -9.5% |
| Flange thickness | 34.5 mm | 40 mm | -13.8% |
| Area | 314.8 cm² | 344 cm² | -8.5% |
| Second moment, major (Iy) | 178,147 cm⁴ | 162,000 cm⁴ | +10.0% |
| Plastic modulus, major (Wpl,y) | 7,079.2 cm³ | 7,090 cm³ | -0.2% |
| Elastic modulus, major (Wel,y) | 6,227.1 cm³ | 6,180 cm³ | +0.8% |
| Second moment, minor (Iz) | 18,106 cm⁴ | 19,200 cm⁴ | -5.7% |
| Plastic modulus, minor (Wpl,z) | 1,769.8 cm³ | 1,930 cm³ | -8.3% |
| Radius of gyration, minor (iz) | 7.59 cm | 7.46 cm | +1.7% |
| Torsion constant (It) | 982.3 cm⁴ | 1,540 cm⁴ | -36.2% |
W 21X166 to AISC Shapes Database v16.0; HE 500 M to EN 10365 · Continental Steel. Difference is expressed relative to HE 500 M.
How to choose between them
On stiffness, W 21X166 has the larger second moment of area: 178,147 cm⁴ against 162,000 cm⁴, a difference of 10.0%. 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 of steel, W 21X166 is the more efficient section: 28.7 against 26.3 cm³ per kg/m, 9.1% 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: HE 500 M has 1930 cm³ of minor-axis plastic modulus against 1769.8 cm³, 8.3% 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.
These come from different catalogues, so treat the swap as a design change rather than a like-for-like substitution. W sections are specified to AISC Shapes Database v16.0 and HE to EN 10365 · Continental Steel; 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 8.5% weight.
In short, HE 500 M is the stronger section and W 21X166 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.