By Priya Nair
Quotes that say "Grade 350" versus "300PLUS" can differ by thousands — and most clients have no idea why. Here's what the numbers mean, when grade matters, and when you're paying for strength you'll never use.
The number is the strength
In Australian structural steel, the grade number is roughly the yield strength in megapascals. Grade 300 (sold as 300PLUS) yields around 300 MPa; Grade 350 yields around 350 MPa — about 15% stronger. Stronger means an engineer can specify a lighter, smaller beam for the same load, which can save steel cost on long spans.
When grade actually matters
For house stumps, fence posts, gates and most farm structures, Grade 300 is plenty and easier on the budget. Grade 350 earns its keep in long-span beams, crane runway steel, multi-storey columns and anywhere deflection is critical. Your engineer decides — our job is to supply, weld and certify exactly what's drawn.
“Never downgrade a grade to save money. If the drawing says 350, there's a calculation behind it.”
Don't forget the coating
- Indoor, dry steel → primer + two-pack paint is plenty
- Outdoor or coastal → hot-dip galvanise, then paint if you want colour
- 316 stainless → within 500m of surf; 304 elsewhere outdoors
Comparing two quotes with different grades or coatings? Send them both over — we'll translate the jargon line by line, free.
PRIYA NAIR
ESTIMATOR & QA LEAD
Priya prices every Ferroforge job and runs our weld QA system. She reads engineers' drawings for fun.
