Steel Grades & Standards
Understanding steel grades helps you choose the right material for your project. This guide explains the common steel grades and standards we supply at Rackerman, what they mean, and where each is typically used. If you're unsure which grade you need, please contact us before ordering — we're happy to help.
What is a steel grade?
A steel grade is a classification that tells you a steel's chemical composition and mechanical properties — in particular its strength. Grades are defined by recognised standards so that a beam or section labelled with a given grade behaves predictably and consistently, wherever it's bought. In the UK and Europe, structural steel grades are set out under the BS EN standards.
Understanding the S235, S275 and S355 grades
The most common structural steel grades you'll see are S235, S275, and S355. The "S" stands for structural steel, and the number is the minimum yield strength in newtons per square millimetre (N/mm² or MPa). A higher number means a stronger steel.
- S235 — minimum yield strength of 235 N/mm². A general-purpose structural steel, commonly used for box and hollow sections, lighter framework, and general fabrication.
- S275 — minimum yield strength of 275 N/mm². A widely used mild steel, common for plate, sheet, and general structural work where moderate strength is needed.
- S355 — minimum yield strength of 355 N/mm². A higher-strength structural steel typically used for universal beams (RSJs) and columns, and load-bearing applications where greater strength is required.
In simple terms: S235 and S275 cover general and moderate-strength uses, while S355 is the go-to for stronger, load-bearing structural members like beams.
What the standards mean (BS EN)
Our structural steel is supplied to relevant BS EN standards, which define the grade, quality, and tolerances of the material:
- BS EN 10025 — the standard covering hot-rolled structural steel products, including the S235, S275, and S355 grades.
- BS EN 10210 / BS EN 10219 — standards covering hot-finished and cold-formed structural hollow sections (box and tube).
You may also see suffixes on a grade, such as JR, J0, or J2 (for example, S355J2). These indicate the steel's impact toughness and the temperature at which it has been tested — relevant where performance in colder conditions matters. If your project specification calls for a particular sub-grade, please let us know and we'll confirm availability.
Grades by product type
- Universal beams (RSJs) and columns — typically supplied in S355, the higher-strength grade suited to load-bearing structural use.
- Mild steel sheet and plate — typically S275.
- Box, rectangular and hollow sections — commonly S235 hollow section grades.
- Stainless steel — supplied in grades such as 304, offering corrosion resistance for applications exposed to moisture or the elements.
- Aluminium (including chequer/durbar plate) — a lightweight, corrosion-resistant alternative where weight saving matters.
Choosing the right grade
The correct grade depends on the load, environment, and purpose of your project. For general fabrication and non-structural work, standard grades are usually sufficient. For anything structural or load-bearing — such as a steel beam supporting a wall or floor — the grade and size must be correct for the load, and we strongly recommend obtaining advice from a structural engineer before ordering. Specifying the wrong grade or size for a load-bearing application can be unsafe.
Need help with specification?
If you're not sure which grade or size you need, we're glad to help point you in the right direction. For load-bearing and structural projects, please use the grade and dimensions specified by your structural engineer. Get in touch with any questions before you order.
Last updated: May 2026