A Simple Guide to Galvanized Steel Grades & Zinc Coatings (Z275, G90, DX51D Explained)

So, you're ready to buy galvanized steel. You look at a quote, and your eyes glaze over. What on earth is DX51D galvanized steel? Is a Z275 coating better than a G90? It feels like you need a secret decoder ring just to place an order.

This is one of the most confusing parts of buying GI steel (Galvanized Iron Steel). But getting it right is critical. Choosing the wrong grade or coating can lead to project failures, budget overruns, and a lot of headaches.

Good news: it's actually much simpler than it looks. In this guide, we'll crack the code for you. We'll explain these terms in plain English so you can buy with confidence and get the perfect material for your job.

New to galvanized steel? Before we dive into the details, you might want to check out our beginner-friendly overview: The Ultimate Guide to Galvanized Steel.

The "Body" vs. The "Raincoat": The Two Parts of Every GI Coil

Think of a galvanized steel coil like a person getting ready for a storm. There are two key parts:

• The Steel Grade (The "Body"): This is the steel itself. It determines the person's physical fitness-are they flexible and agile, or are they a strong, muscular powerlifter?
• The Zinc Coating (The "Raincoat"): This is the protective zinc layer. It determines how thick and waterproof their raincoat is.

You need the right body and the right raincoat for the job. Let's look at the body first.

Decoding the Steel Grades: How "Soft" or "Strong" is Your Steel?

The grade tells you about the steel's mechanical properties, mainly its strength and ductility (how easy it is to bend).

Commercial Quality (CQ)-The Flexible Workhorse

This is the most common type of grade you'll encounter. Think of it as the agile athlete. It's designed to be bent, pressed, stamped, and roll-formed without cracking.

• DX51D (European Standard EN 10346): This is the go-to grade for general-purpose applications in Europe, Africa, and many other parts of the world. The "D" stands for "Drawing," meaning it's great for forming.
• SGCC (Japanese Standard JIS G3302): This is the equivalent you'll often see in Asia. It's also a soft, highly formable grade.

Best for: Roofing, wall cladding, HVAC ducts, appliance casings, and pretty much any application that requires shaping the galvanized steel.

Structural Quality (SQ)-For When You Need Strength

This is the powerlifter. Structural grades (like S280GD or S350GD) have a higher yield strength, meaning they are much stronger and designed to bear loads. They are less flexible than commercial grades.

Best for: Steel purlins, floor decking, and other structural components.

Choosing the wrong grade can be a costly mistake. Using a structural grade for roofing will make forming difficult, while using a commercial grade for a purlin is a safety risk.
Not sure which one you need? [Talk to our experts]. We'll help you match the right grade to your project, saving you time and money.

Decoding the Zinc Coating: How Thick is Your "Raincoat"?

The zinc coating is your first line of defense against rust-a key factor in Galvanized Steel Corrosion Resistance. The rule is simple: the thicker the coating, the longer it lasts.

Understanding the Numbers: Z275, G90, and What They Mean

You'll see the coating specified in two main ways:

Metric (g/m²): Used by most of the world (EN, JIS standards). It means grams of zinc per square meter (total for both sides).

Z275 galvanized steel means 275 g/m² of zinc. This is a very common and durable coating for outdoor use.

A Z180 coating (180 g/m²) is lighter, and a Z100 coating (100 g/m²) is even lighter.

Imperial (oz/ft²): Used mainly in North America (ASTM standards).

G90 steel coating is the most common specification. It's very similar in thickness and performance to Z275.

Other common grades are G60 (similar to Z180) and G30 (similar to Z100).

Practical Guide: How to Choose the Right Zinc Coating

Here's a simple cheat sheet to help you choose:

Common Standards & Grades of Galvanized Steel

Galvanized Coating Thickness (per side, g/m²)

We offer a full range of zinc coatings from light Z60 to heavy-duty Z275 and beyond. We can customize the "raincoat" to perfectly match your climate and budget.
[Get a Quick Quote] on your required zinc coating today!

Putting It All Together: Winning Combinations for Your Application

For Durable Roofing & Cladding:

The market's gold standard is DX51D + Z275 (or G90). This combination gives you excellent formability and long-lasting weather protection-ideal for maximizing Galvanized Steel Corrosion Resistance.

For Interior Light Steel Framing:

DX51D + Z80 is the smart, cost-effective choice. You get the formability you need with enough protection for an indoor environment.

For Home Appliances:

SGCC + Z100 Zero Spangle is perfect. The SGCC grade is easy to stamp into complex shapes, and the smooth, spangle-free surface is ready for a beautiful paint finish-a top pick for Electro-Galvanized (EGI)-related appliance uses.

Don't Guess, Get Expert Advice

Understanding steel grades and zinc coatings is the key to controlling your project's quality, lifespan, and cost. Now you have the knowledge to read the specifications like a pro.