RHS 300×250×6.3 vs RHS 300×200×8
RHS 300×250×6.3 is an RHS Hot-finished section from the UK Blue Book (SCI P363); RHS 300×200×8 is the closest equivalent in the European (Continental) range. RHS 300×200×8 carries more bending: 757 cm³ of plastic modulus against 716 cm³, 5.4% more. RHS 300×250×6.3 is the lighter of the two at 52.8 kg/m against 59.1 kg/m, a saving of 10.7% on steel weight. Both are about 300 mm deep, so either fits the same construction zone.
| Property | RHS 300×250×6.3 RHS Hot-finished | RHS 300×200×8 RHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 52.8 kg/m | 59.1 kg/m | -10.7% |
| Depth | 300 mm | 300 mm | same |
| Width | 250 mm | 200 mm | +25.0% |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 67.3 cm² | 75.2 cm² | -10.5% |
| Second moment, major (Iy) | 9,190 cm⁴ | 9,389 cm⁴ | -2.1% |
| Plastic modulus, major (Wpl,y) | 716 cm³ | 757 cm³ | -5.4% |
| Elastic modulus, major (Wel,y) | 613 cm³ | 626 cm³ | -2.1% |
| Second moment, minor (Iz) | 6,950 cm⁴ | 5,042 cm⁴ | +37.8% |
| Plastic modulus, minor (Wpl,z) | 633 cm³ | 574 cm³ | +10.3% |
| Radius of gyration, minor (iz) | 10.2 cm | 8.19 cm | +24.5% |
| Torsion constant (It) | 12,200 cm⁴ | 10,630 cm⁴ | +14.8% |
RHS 300×250×6.3 to BS EN 10210-2:2006; RHS 300×200×8 to EN 10219 · Continental Steel. Difference is expressed relative to RHS 300×200×8.
How to choose between them
On stiffness, RHS 300×200×8 has the larger second moment of area: 9,389 cm⁴ against 9,190 cm⁴, a difference of 2.1%. 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 300×250×6.3 is the more efficient section: 13.6 against 12.8 cm³ per kg/m, 5.9% 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 300×250×6.3 has 633 cm³ of minor-axis plastic modulus against 574 cm³, 10.3% 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 10.7% weight.
In short, RHS 300×200×8 is the stronger section and RHS 300×250×6.3 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.