W 21X68 vs IPE O 500
W 21X68 is an W section from the American AISC Shapes Database; IPE O 500 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 2621.9 cm³ against 2610 cm³ of plastic modulus, a difference of 0.5%. W 21X68 is the lighter of the two at 101.2 kg/m against 107 kg/m, a saving of 5.4% on steel weight. W 21X68 is deeper, 535.9 mm against 506 mm, which matters where the floor zone is tight.
| Property | W 21X68 W | IPE O 500 IPE | Difference |
|---|---|---|---|
| Mass | 101.2 kg/m | 107 kg/m | -5.4% |
| Depth | 535.9 mm | 506 mm | +5.9% |
| Width | 210.1 mm | 202 mm | +4.0% |
| Web thickness | 10.9 mm | 12 mm | -9.2% |
| Flange thickness | 17.4 mm | 19 mm | -8.4% |
| Area | 129 cm² | 137 cm² | -5.8% |
| Second moment, major (Iy) | 61,602 cm⁴ | 57,800 cm⁴ | +6.6% |
| Plastic modulus, major (Wpl,y) | 2,621.9 cm³ | 2,610 cm³ | +0.5% |
| Elastic modulus, major (Wel,y) | 2,294.2 cm³ | 2,280 cm³ | +0.6% |
| Second moment, minor (Iz) | 2,693 cm⁴ | 2,620 cm⁴ | +2.8% |
| Plastic modulus, minor (Wpl,z) | 399.84 cm³ | 409 cm³ | -2.2% |
| Radius of gyration, minor (iz) | 4.57 cm | 4.38 cm | +4.3% |
| Torsion constant (It) | 102 cm⁴ | 143 cm⁴ | -28.7% |
W 21X68 to AISC Shapes Database v16.0; IPE O 500 to EN 10365 · Continental Steel. Difference is expressed relative to IPE O 500.
How to choose between them
On stiffness, W 21X68 has the larger second moment of area: 61,602 cm⁴ against 57,800 cm⁴, a difference of 6.6%. 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 21X68 is the more efficient section: 25.9 against 24.4 cm³ per kg/m, 6.2% 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.
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 IPE 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 5.4% weight.
In short, W 21X68 is the stronger section and W 21X68 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.