The Mohs Scale: How Hard Is Your Metal?
16 Sep 2025
Think metal’s just metal? Think again. From soft-as-butter aluminium to rock-hard tungsten, metal hardness varies massively – and it matters more than you might think. Whether you’re welding, machining, building or bolting, picking the right metal for the job starts with knowing how tough it is.
That’s where hardness scales come in. And one of the most well-known is the Mohs scale. In this guide, we’ll break down how the Mohs scale works, what it means for metal and why alternative metal hardness scales might give you a clearer picture – especially when you’re working with industrial-grade kit.
Article in Brief
The Mohs scale ranks material hardness from 1 (soft) to 10 (hard).
It’s useful but not perfect – especially when it comes to metals.
Scales like Rockwell and Vickers offer more precise results.
Knowing where a material sits on the scale of hardness for metals helps you choose the right material for the job.
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What is the Mohs scale?
Back in 1812, Friedrich Mohs (an Austrian geologist) developed a way to measure how easily one material could scratch another. Known as the Mohs hardness scale, it places materials on a simple 1-10 scale. Talc scores 1 (softest), and diamond sits at 10 (hardest).
While it was made for minerals, it’s often applied (albeit loosely) to metals. That’s where things get interesting.
Where metals land on the Mohs scale
Metals don’t always behave like minerals. They bend. They harden under pressure. And some resist scratches better after heat treatment. But for a quick comparison, the Mohs scale of hardness for metals still comes in handy.
Here’s a rough metal hardness chart for common materials:
- Aluminium, 2.5 – Lightweight and easy to work with. Great for aerospace, construction and more.
- Copper, 3 – Soft, ductile and perfect for wires and plumbing. (Copper on the Mohs hardness scale is relatively low.)
- Brass, 3-4 – Harder than copper. Its mix of durability and looks makes it ideal for fittings, instruments and more. (Brass’s Mohs hardness value makes it good for decorative metalwork.)
- Bronze, 3-4 – Similar to brass, but with better wear resistance – great for marine gear and sculptures.
- Cast Iron, 4.5 – Brittle but strong. Often found in cookware and engine blocks.
- Mild Steel 4-8 – Varies based on treatment. It’s the most commonly used structural metal. (Steel Mohs hardness depends on how it’s made. Untreated mild steel is closer to 4, while hardened/high-carob steels can move higher. )
- Stainless Steel, 5-6 – Strong, corrosion-resistant and reliable. Stainless steel’s Mohs hardness is higher than mild steel, which makes it better for tough environments. Not all stainless steels sit at 5-6 though, some grades are softer and some harder.
- Titanium, 6 – Lightweight but hard. Used in aerospace and implants. (Titanium’s Mohs scale value shows its toughness and low weight combo.)
- Tungsten, 7.5 – Pure tungsten’s Mohs scale score is ~7.5, but in practice it’s usually alloyed. Tungsten carbide is ~ 9 Mohs. It's almost as hard as it gets. Used in tools, mining equipment and armour.
The problem with Mohs for metals
The Mohs metal hardness scale is good for basic scratch resistance – but metals are more complex. They're malleable. They deform. And some get harder with use or treatment. That’s why engineers prefer more exact tests.
Enter Rockwell, Brinell and Vickers.
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Better hardness tests for serious jobs
1. Rockwell Hardness
Tests how deep an indenter pushes into the metal. Quick and reliable.
- HRB – Great for aluminium and softer steels.
- HRC – Designed for harder metals like hardened steel.
Perfect for comparing grades of industrial metal.
2. Brinell Hardness Number (BHN)
Uses a ball to press into the surface and measures the dent.
- Works on rough surfaces or large parts. Think castings, forgings and sheet.
Good for comparing data on a metal hardness table.
3. Vickers Hardness Number (VHN)
A precision test. Uses a diamond tip and a microscope. Excellent for micro-parts and coatings.
Need to match a value from a hardness chart for metal? Vickers will probably be your best bet.
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Hardness matters in the real world
Here’s how metal hardness affects your work:
- Machining – Softer metals are easier to cut. Harder ones last longer.
- Tooling – A carbide plate needs to be harder than the material it’s shaping.
- Construction – Pick the right Mohs hardness scale value to avoid bending or failure.
- Welding – Different hardness = different results when heating or joining.
And don’t forget, hardness affects wear resistance, safety and longevity.
What affects a metal’s hardness?
- Heat treatment – Quenching or tempering steel changes its Mohs rating.
- Alloying – Adding elements like vanadium or chromium alters hardness.
- Work hardening – Cold-working boosts toughness.
So when checking the hardness of steel on the Mohs scale, remember – not all steel is created equal.
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Still unsure which metal to pick?
It’s not just about how hard a metal is. It’s also about how easy it is to work with, how long it lasts and whether it’s right for your job.
Use a metal hardness chart, but also think about your tools, your budget and how you plan to use the metal.
For example:
- Need strong but lightweight? Go for titanium for a high-grade Mohs hardness material.
- Want something soft but conductive? Copper’s hardness on the Mohs scale tells you it’s easy to shape but scratches easily.
- Looking for something tougher than brass? Check the brass scale and compare it to bronze or stainless.
Get your metal – cut to size and ready to go
At The Metal Store, we make metal buying easy. Whether you’re after hard-as-nails stainless or easy-to-weld mild steel, we’ve got you covered.
We stock everything from aluminium to high-performance steels and alloys. There’s no minimum order with free cutting on most of our products.
Don’t guess. Know your metal. Use our handy metal hardness scale references or get in touch for expert advice. Order online today and get your metal delivered when you need it – without the hassle.
