RHS 250×100×8 vs RHS 250×150×6.3
RHS 250×100×8 is an RHS Hot-finished section from the UK Blue Book (SCI P363); RHS 250×150×6.3 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 404 cm³ against 402 cm³ of plastic modulus, a difference of 0.5%. RHS 250×150×6.3 is the lighter of the two at 38 kg/m against 41.4 kg/m, a saving of 8.9% on steel weight. Both are about 250 mm deep, so either fits the same construction zone.
| Property | RHS 250×100×8 RHS Hot-finished | RHS 250×150×6.3 RHS | Difference |
|---|---|---|---|
| Mass | 41.4 kg/m | 38 kg/m | +8.9% |
| 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 | 52.8 cm² | 48.4 cm² | +9.1% |
| Second moment, major (Iy) | 3,940 cm⁴ | 4,143 cm⁴ | -4.9% |
| Plastic modulus, major (Wpl,y) | 404 cm³ | 402 cm³ | +0.5% |
| Elastic modulus, major (Wel,y) | 315 cm³ | 331 cm³ | -4.8% |
| Second moment, minor (Iz) | 909 cm⁴ | 1,874 cm⁴ | -51.5% |
| Plastic modulus, minor (Wpl,z) | 209 cm³ | 283 cm³ | -26.1% |
| Radius of gyration, minor (iz) | 4.15 cm | 6.22 cm | -33.3% |
| Torsion constant (It) | 2,430 cm⁴ | 4,054 cm⁴ | -40.1% |
RHS 250×100×8 to BS EN 10210-2:2006; RHS 250×150×6.3 to EN 10219 · Continental Steel. Difference is expressed relative to RHS 250×150×6.3.
How to choose between them
On stiffness, RHS 250×150×6.3 has the larger second moment of area: 4,143 cm⁴ against 3,940 cm⁴, a difference of 4.9%. 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 250×150×6.3 is the more efficient section: 10.6 against 9.8 cm³ per kg/m, 7.8% 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 250×150×6.3 has 283 cm³ of minor-axis plastic modulus against 209 cm³, 26.1% 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 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 8.9% weight.
In short, RHS 250×100×8 is the stronger section and RHS 250×150×6.3 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.