W 21X275 vs HE 600 x 399
W 21X275 is an W section from the American AISC Shapes Database; HE 600 x 399 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 12273.9 cm³ against 12500 cm³ of plastic modulus, a difference of 1.8%. HE 600 x 399 is the lighter of the two at 399 kg/m against 409.2 kg/m, a saving of 2.6% on steel weight. HE 600 x 399 is deeper, 648 mm against 612.1 mm, which matters where the floor zone is tight.
| Property | W 21X275 W | HE 600 x 399 HE | Difference |
|---|---|---|---|
| Mass | 409.2 kg/m | 399 kg/m | +2.6% |
| Depth | 612.1 mm | 648 mm | -5.5% |
| Width | 327.7 mm | 315 mm | +4.0% |
| Web thickness | 31 mm | 30 mm | +3.3% |
| Flange thickness | 55.6 mm | 54 mm | +3.0% |
| Area | 527.7 cm² | 508 cm² | +3.9% |
| Second moment, major (Iy) | 320,082 cm⁴ | 345,000 cm⁴ | -7.2% |
| Plastic modulus, major (Wpl,y) | 12,273.9 cm³ | 12,500 cm³ | -1.8% |
| Elastic modulus, major (Wel,y) | 10,454.9 cm³ | 10,600 cm³ | -1.4% |
| Second moment, minor (Iz) | 32,757 cm⁴ | 28,300 cm⁴ | +15.7% |
| Plastic modulus, minor (Wpl,z) | 3,129.9 cm³ | 2,810 cm³ | +11.4% |
| Radius of gyration, minor (iz) | 7.87 cm | 7.46 cm | +5.5% |
| Torsion constant (It) | 4,454 cm⁴ | 3,930 cm⁴ | +13.3% |
W 21X275 to AISC Shapes Database v16.0; HE 600 x 399 to EN 10365 · Continental Steel. Difference is expressed relative to HE 600 x 399.
How to choose between them
On stiffness, HE 600 x 399 has the larger second moment of area: 345,000 cm⁴ against 320,082 cm⁴, a difference of 7.2%. 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, HE 600 x 399 is the more efficient section: 31.3 against 30.0 cm³ per kg/m, 4.3% 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 21X275 has 3129.9 cm³ of minor-axis plastic modulus against 2810 cm³, 11.4% 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 2.6% weight.
In short, HE 600 x 399 is the stronger section and HE 600 x 399 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.