Steel Plate Grades Explained – DD11 vs S275 vs S355 (Ireland)
Which mild steel plate should you use? A clear comparison of grades, thicknesses and weights, plus chequer, wear and weathering plate, from Heiton Steel.
What do the steel plate grade codes mean?
- DD11 – “Drawing Deep” grade to EN 10111, a hot-rolled low-carbon steel made for cold forming, bending and pressing. Good ductility, not specified by yield strength.
- S275 – structural steel to EN 10025 with a minimum yield strength of 275 N/mm². A reliable general-purpose structural plate.
- S355 – structural steel to EN 10025 with a minimum yield strength of 355 N/mm². Stronger, so you can often use a thinner plate for the same load.
In short: S is for “structural” and the number is the yield strength. A higher number means more strength.
DD11 vs S275 vs S355 at a glance
| Grade | Standard | Min yield | Best for |
|---|---|---|---|
| DD11 | EN 10111 | Not specified | Forming, bending, pressing, general fabrication |
| S275 | EN 10025 | 275 N/mm² | General structural and load-bearing work |
| S355 | EN 10025 | 355 N/mm² | Heavier structural loads, thinner sections |
How much does steel plate weigh?
Mild steel weighs roughly 7.85 kg/m² for every 1 mm of thickness (density 7,850 kg/m³). Use the table below for common thicknesses.
| Thickness (mm) | Weight (kg/m²) | Per 2.5 × 1.25 m sheet (kg) |
|---|---|---|
| 3 | 23.55 | 73.6 |
| 5 | 39.25 | 122.7 |
| 6 | 47.10 | 147.2 |
| 8 | 62.80 | 196.2 |
| 10 | 78.50 | 245.3 |
| 12 | 94.20 | 294.4 |
| 15 | 117.75 | 368.0 |
| 20 | 157.00 | 490.6 |
| 25 | 196.25 | 613.3 |
Formula: weight (kg) = length (m) × width (m) × thickness (mm) × 7.85.
Specialist plates we stock
- Chequer Plate – raised pattern for anti-slip floors, walkways, ramps and steps.
- Wear Plate 400 – abrasion-resistant plate (~400 HB) for buckets, liners, chutes and high-wear areas.
- Weathering Plate – forms a stable rust-coloured patina, popular for architectural and outdoor features.
- CR4 – cold-reduced sheet with a smooth finish, ideal for forming and visible surfaces.
- Galv Flat Sheet (Lock Forming) and Zintec – galvanised and zinc-coated sheet for corrosion resistance.
See the full plate range, including hot rolled mild steel plate in DD11, S275 and S355.
Which grade should I choose?
- Folding, pressing or forming a part? Choose DD11.
- Standard structural brackets, base plates and gussets? S275 is usually fine.
- Heavier loads, or you want to save weight with a thinner plate? Choose S355.
- Anti-slip flooring? Chequer plate. High abrasion? Wear Plate 400.
If in doubt, send us your drawing or application and we will recommend the right grade and thickness.
How to order
We stock the full plate range and can help you choose the right grade and thickness for your job. Order in three steps:
- Tell us grade, thickness and the size or quantity you need.
- Confirm your delivery branch or site.
- We quote competitively and arrange next-working-day delivery with live tracking where available.
Frequently asked questions
What is the difference between S275 and S355 steel?
Both are structural mild steels. The number is the minimum yield strength in N/mm², so S355 (355) is stronger than S275 (275) and often lets you specify a thinner, lighter plate for the same load.
Is DD11 the same as mild steel?
DD11 is a low-carbon mild steel, but it is graded for forming rather than by yield strength. It bends and presses well, which is why it is used for formed parts rather than primary structural members.
How do I calculate the weight of a steel plate?
Multiply length (m) × width (m) × thickness (mm) × 7.85. For example, a 2 m × 1 m × 10 mm plate weighs 2 × 1 × 10 × 7.85 = 157 kg.
Does grade change the weight of the plate?
No. DD11, S275 and S355 all have essentially the same density, so weight depends on size and thickness, not grade.