RHS 300×150×14.2 vs CF RHS 300×200×12.5
RHS 300×150×14.2 is an RHS Hot-finished section from the UK Blue Book (SCI P363); CF RHS 300×200×12.5 is the closest equivalent in the UK Blue Book (SCI P363). They are close to interchangeable in bending: 1100 cm³ against 1090 cm³ of plastic modulus, a difference of 0.9%. CF RHS 300×200×12.5 is the lighter of the two at 88 kg/m against 92.3 kg/m, a saving of 4.9% on steel weight. Both are about 300 mm deep, so either fits the same construction zone.
| Property | RHS 300×150×14.2 RHS Hot-finished | CF RHS 300×200×12.5 RHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 92.3 kg/m | 88 kg/m | +4.9% |
| Depth | 300 mm | 300 mm | same |
| Width | 150 mm | 200 mm | -25.0% |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 118 cm² | 112 cm² | +5.4% |
| Second moment, major (Iy) | 12,900 cm⁴ | 13,200 cm⁴ | -2.3% |
| Plastic modulus, major (Wpl,y) | 1,100 cm³ | 1,090 cm³ | +0.9% |
| Elastic modulus, major (Wel,y) | 862 cm³ | 879 cm³ | -1.9% |
| Second moment, minor (Iz) | 4,230 cm⁴ | 7,060 cm⁴ | -40.1% |
| Plastic modulus, minor (Wpl,z) | 666 cm³ | 828 cm³ | -19.6% |
| Radius of gyration, minor (iz) | 6 cm | 7.94 cm | -24.4% |
| Torsion constant (It) | 10,500 cm⁴ | 15,800 cm⁴ | -33.5% |
RHS 300×150×14.2 to BS EN 10210-2:2006; CF RHS 300×200×12.5 to BS EN 10219-2:2006. Difference is expressed relative to CF RHS 300×200×12.5.
How to choose between them
On stiffness, CF RHS 300×200×12.5 has the larger second moment of area: 13,200 cm⁴ against 12,900 cm⁴, a difference of 2.3%. 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, CF RHS 300×200×12.5 is the more efficient section: 12.4 against 11.9 cm³ per kg/m, 3.8% 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: CF RHS 300×200×12.5 has 828 cm³ of minor-axis plastic modulus against 666 cm³, 19.6% 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, RHS 300×150×14.2 is the stronger section and CF RHS 300×200×12.5 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.