RHS 300×200×6.3 vs CF RHS 300×100×10
RHS 300×200×6.3 is an RHS Hot-finished section from the UK Blue Book (SCI P363); CF RHS 300×100×10 is the closest equivalent in the UK Blue Book (SCI P363). They are close to interchangeable in bending: 624 cm³ against 631 cm³ of plastic modulus, a difference of 1.1%. RHS 300×200×6.3 is the lighter of the two at 47.9 kg/m against 57 kg/m, a saving of 16.0% on steel weight. Both are about 300 mm deep, so either fits the same construction zone.
| Property | RHS 300×200×6.3 RHS Hot-finished | CF RHS 300×100×10 RHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 47.9 kg/m | 57 kg/m | -16.0% |
| Depth | 300 mm | 300 mm | same |
| Width | 200 mm | 100 mm | +100.0% |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 61 cm² | 72.6 cm² | -16.0% |
| Second moment, major (Iy) | 7,830 cm⁴ | 7,110 cm⁴ | +10.1% |
| Plastic modulus, major (Wpl,y) | 624 cm³ | 631 cm³ | -1.1% |
| Elastic modulus, major (Wel,y) | 522 cm³ | 474 cm³ | +10.1% |
| Second moment, minor (Iz) | 4,190 cm⁴ | 1,220 cm⁴ | +243.4% |
| Plastic modulus, minor (Wpl,z) | 472 cm³ | 285 cm³ | +65.6% |
| Radius of gyration, minor (iz) | 8.29 cm | 4.11 cm | +101.7% |
| Torsion constant (It) | 8,480 cm⁴ | 3,680 cm⁴ | +130.4% |
RHS 300×200×6.3 to BS EN 10210-2:2006; CF RHS 300×100×10 to BS EN 10219-2:2006. Difference is expressed relative to CF RHS 300×100×10.
How to choose between them
On stiffness, RHS 300×200×6.3 has the larger second moment of area: 7,830 cm⁴ against 7,110 cm⁴, a difference of 10.1%. 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 300×200×6.3 is the more efficient section: 13.0 against 11.1 cm³ per kg/m, 17.7% 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 300×200×6.3 has 472 cm³ of minor-axis plastic modulus against 285 cm³, 65.6% 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, CF RHS 300×100×10 is the stronger section and RHS 300×200×6.3 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.