RHS 200×150×6.3 vs RHS 200×100×9
RHS 200×150×6.3 is an RHS Hot-finished section from the UK Blue Book (SCI P363); RHS 200×100×9 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 289 cm³ against 293 cm³ of plastic modulus, a difference of 1.4%. RHS 200×150×6.3 is the lighter of the two at 33 kg/m against 40.52 kg/m, a saving of 18.6% on steel weight. Both are about 200 mm deep, so either fits the same construction zone.
| Property | RHS 200×150×6.3 RHS Hot-finished | RHS 200×100×9 RHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 33 kg/m | 40.5 kg/m | -18.6% |
| Depth | 200 mm | 200 mm | same |
| Width | 150 mm | 100 mm | +50.0% |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 42.1 cm² | 48 cm² | -12.3% |
| Second moment, major (Iy) | 2,420 cm⁴ | 2,276 cm⁴ | +6.3% |
| Plastic modulus, major (Wpl,y) | 289 cm³ | 293 cm³ | -1.4% |
| Elastic modulus, major (Wel,y) | 242 cm³ | 228 cm³ | +6.1% |
| Second moment, minor (Iz) | 1,550 cm⁴ | 764 cm⁴ | +102.9% |
| Plastic modulus, minor (Wpl,z) | 237 cm³ | 180 cm³ | +31.7% |
| Radius of gyration, minor (iz) | 6.07 cm | 3.99 cm | +52.1% |
| Torsion constant (It) | 2,950 cm⁴ | 1,988 cm⁴ | +48.4% |
RHS 200×150×6.3 to BS EN 10210-2:2006; RHS 200×100×9 to EN 10219 · Continental Steel. Difference is expressed relative to RHS 200×100×9.
How to choose between them
On stiffness, RHS 200×150×6.3 has the larger second moment of area: 2,420 cm⁴ against 2,276 cm⁴, a difference of 6.3%. 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, RHS 200×150×6.3 is the more efficient section: 8.8 against 7.2 cm³ per kg/m, 21.1% 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: RHS 200×150×6.3 has 237 cm³ of minor-axis plastic modulus against 180 cm³, 31.7% 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. RHS Hot-finished sections are specified to BS EN 10210-2:2006 and RHS Cold-formed to EN 10219 · 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 18.6% weight.
In short, RHS 200×100×9 is the stronger section and RHS 200×150×6.3 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.