S275 vs S355 — Which Steel Grade Do You Need?

If you've seen "S275" or "S355" on a steel drawing and wondered what it means, here's the plain version.

What the grade actually means

Both are structural steel grades to EN 10025. The number is the minimum yield strength in N/mm² — roughly, how much stress the steel takes before it starts to permanently deform:

• S275 — yields at about 275 N/mm². The long-standing general-purpose grade for everyday structural work.
• S355 — yields at about 355 N/mm². Around 30% stronger, so it carries more load, or lets you use a smaller, lighter section for the same load.

When each is used

S275 is fine for a huge amount of domestic and light structural work. S355 comes into its own on longer spans, heavier loads, or where keeping the beam depth or weight down matters — larger openings, commercial frames, transfer beams. Using the higher grade can sometimes save weight (and cost) even though it's dearer per tonne.

Don't guess — follow the spec

The grade is chosen by whoever designed the structure. Build to the drawing: if it says S355, use S355. Mixing grades or substituting a weaker one is not safe.

Both in stock, with mill certs

Leinster Steel holds both S275 and S355, cut to length, black or primed, with mill test certificates as standard so the grade is traceable. Get an instant price or send your cut list.

General information only — follow your structural engineer's specification for grade and section.