RHS 250×100×16 vs RHS 250×150×12.5
RHS 250×100×16 is an RHS Hot-finished section from the UK Blue Book (SCI P363); RHS 250×150×12.5 is the closest equivalent in the European (Continental) range. RHS 250×100×16 carries more bending: 719 cm³ of plastic modulus against 678 cm³, 6.0% more. RHS 250×150×12.5 is the lighter of the two at 68.3 kg/m against 77.7 kg/m, a saving of 13.8% on steel weight. Both are about 250 mm deep, so either fits the same construction zone.
| Property | RHS 250×100×16 RHS Hot-finished | RHS 250×150×12.5 RHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 77.7 kg/m | 68.3 kg/m | +13.8% |
| 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 | 99 cm² | 87 cm² | +13.8% |
| Second moment, major (Iy) | 6,690 cm⁴ | 6,633 cm⁴ | +0.9% |
| Plastic modulus, major (Wpl,y) | 719 cm³ | 678 cm³ | +6.0% |
| Elastic modulus, major (Wel,y) | 535 cm³ | 531 cm³ | +0.8% |
| Second moment, minor (Iz) | 1,430 cm⁴ | 3,002 cm⁴ | -52.4% |
| Plastic modulus, minor (Wpl,z) | 358 cm³ | 477 cm³ | -24.9% |
| Radius of gyration, minor (iz) | 3.8 cm | 5.87 cm | -35.3% |
| Torsion constant (It) | 4,050 cm⁴ | 7,315 cm⁴ | -44.6% |
RHS 250×100×16 to BS EN 10210-2:2006; RHS 250×150×12.5 to EN 10219 · Continental Steel. Difference is expressed relative to RHS 250×150×12.5.
How to choose between them
On stiffness, RHS 250×100×16 has the larger second moment of area: 6,690 cm⁴ against 6,633 cm⁴, a difference of 0.9%. 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 250×150×12.5 is the more efficient section: 9.9 against 9.3 cm³ per kg/m, 6.8% 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: RHS 250×150×12.5 has 477 cm³ of minor-axis plastic modulus against 358 cm³, 24.9% 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.
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 13.8% weight.
In short, RHS 250×100×16 is the stronger section and RHS 250×150×12.5 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.