RHS 250×100×12.5 vs CF RHS 250×150×10
RHS 250×100×12.5 is an RHS Hot-finished section from the UK Blue Book (SCI P363); CF RHS 250×150×10 is the closest equivalent in the UK Blue Book (SCI P363). They are close to interchangeable in bending: 592 cm³ against 582 cm³ of plastic modulus, a difference of 1.7%. CF RHS 250×150×10 is the lighter of the two at 57 kg/m against 62.5 kg/m, a saving of 9.6% on steel weight. Both are about 250 mm deep, so either fits the same construction zone.
| Property | RHS 250×100×12.5 RHS Hot-finished | CF RHS 250×150×10 RHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 62.5 kg/m | 57 kg/m | +9.6% |
| Depth | 250 mm | 250 mm | same |
| Width | 100 mm | 150 mm | -33.3% |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 79.6 cm² | 72.6 cm² | +9.6% |
| Second moment, major (Iy) | 5,620 cm⁴ | 5,830 cm⁴ | -3.6% |
| Plastic modulus, major (Wpl,y) | 592 cm³ | 582 cm³ | +1.7% |
| Elastic modulus, major (Wel,y) | 450 cm³ | 466 cm³ | -3.4% |
| Second moment, minor (Iz) | 1,250 cm⁴ | 2,630 cm⁴ | -52.5% |
| Plastic modulus, minor (Wpl,z) | 299 cm³ | 409 cm³ | -26.9% |
| Radius of gyration, minor (iz) | 3.96 cm | 6.02 cm | -34.2% |
| Torsion constant (It) | 3,440 cm⁴ | 6,120 cm⁴ | -43.8% |
RHS 250×100×12.5 to BS EN 10210-2:2006; CF RHS 250×150×10 to BS EN 10219-2:2006. Difference is expressed relative to CF RHS 250×150×10.
How to choose between them
On stiffness, CF RHS 250×150×10 has the larger second moment of area: 5,830 cm⁴ against 5,620 cm⁴, a difference of 3.6%. 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, CF RHS 250×150×10 is the more efficient section: 10.2 against 9.5 cm³ per kg/m, 7.2% 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.
The two diverge much more about the minor axis: CF RHS 250×150×10 has 409 cm³ of minor-axis plastic modulus against 299 cm³, 26.9% 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 250×100×12.5 is the stronger section and CF RHS 250×150×10 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.