Metal Hardness Scale: 4 Main Types Explained (2026 Guide)

Metal hardness is a metal’s resistance to deformation and scratching. A metal’s bonding mechanism determines its hardness.

A scale helps specify a metal’s hardness. A higher number indicates greater hardness. There are a few types of hardness scales. For example, the Rockwell scale includes HRB and HRC, the Brinell scale includes HB, and there are Vickers and Mohs scratch scales. Since these scales don’t measure the same things, we cannot directly compare their values to one another.

You’ve likely noticed a specification like 58–62 HRC or a chart that shows the same metal at three different hardness ratings. Most charts don’t list the scale, the condition under which the number was measured, or whether the number can even be accurately converted. This 2026 guide will show you how each scale is tested, where metals usually fall, and how to properly compare the numbers without being misled.

Main Points

● You measure the ability of a metal to resist the flow of electrons. The following are some hardness tests.

● The three most common indentation hardness tests that metals are subjected to are the Rockwell, Brinell and Vickers tests.

● The Rockwell B scale is better suited to soft metals like copper alloys and aluminum, whereas the Rockwell C scale is better suited to hardened steels. Furthermore, the HRC scale ranges from 20 to 70.

● The Mohs scale is good for comparing the hardness of a series of minerals, but not for comparing the hardness of two materials.

● The conversion tables are little more than a guide, and the ASTM tables only work for fixed materials.

● The correct scales depend on the part and material: Rockwell for fast testing, Brinell for castings or forgings, and Vickers for thin sections, coatings or microhardness.

● When a hardness number is read, it is necessary to know the scale, load and condition of the material; hence, all three things should be considered.

What does a metal hardness scale indicate, and how is it represented?

A metal hardness scale measures a metal’s ability to withstand permanent deformation from indentation or scratching. There is more than one because each test determines the metal’s resistance to indentation or scratching using a different method.

The scale mainly consists of:

● The Mohs scale determines which materials can scratch others.

● A hard tip is pressed into the surface, and we measure the depth (in the case of Rockwell) or the size of the indentation (in the case of Brinell and Vickers).

● Rebound hardness: How fast a dropped impact body bounces back is measured by the Leeb test and reported as HLD.

Suppose a person needs to find out the depth of a hole, they will always be given a depth reading and never any other kind of reading. A depth reading, a dent-width reading, and a rebound reading are three different numbers. A number from one family of numbers is just a translation of another, never the same individual number. Hence, one could be told by an information sheet that 95 HB and 60 HRB refer to the same aluminum.

Two other indentation tests suitable for special applications include the Knoop test (HK) for very thin or brittle samples, using an elongated diamond point, and Lee’s method, which is applicable to parts too large to be transported to a lab.

Can metal hardness be determined using the Mohs scale?

Yes, but its results are too rough for any engineering uses. The Mohs scale was invented by Friedrich Mohs in 1812. It grades minerals from 1, for talc, to 10, for diamond. However, it is still considered too rough for measuring the hardness of industrial metals, as of 2026. Source

The way to make sense of whether a material is hard is basic. The hardness of the material can be compared with that of solid tungsten carbide plates. One can look at the relative hardness of various materials by simply trying to scratch them with one of the plates.

The issue is illustrated by the range across sources. Metal Supermarkets lists steel as a 4 (Metal Supermarkets, circa 2022); Rivcut rates it at 5 (Rivcut 2026); and The Metal Store rates it from 4 to 8 (The Metal Store, undated). Four to eight spans four of the nine steps between 1 and 10, or 44% of the scale, for a single material family.

The hardness, ductility and work-hardening of metals make them difficult to place accurately on the Mohs scale. We were given the Mohs values of pure metals in class, but what would happen if the metals or alloys were treated?

What Are the Principles of the Rockwell, Brinell, and Vickers Hardness Tests?

Rockwell, Brinell, and Vickers are the three main indentation tests for metals. They are characterized by their indenter and applied load. The major standards are ASTM E18 (Rockwell), E10 (Brinell), E92 (Vickers macro), E384 (Vickers and Knoop micro), and E140 (conversion tables) ([Infinita Lab, 2026]).

HRB and HRC are Rockwell hardness scales.

The Rockwell hardness test measures the depth of penetration of an indenter under a large load. The B scale employs a 1/16-inch steel ball under an applied load of 100 kgf and is used for testing relatively soft materials, such as copper alloys, soft steels and aluminum alloys. The C scale employs a 120-degree diamond cone under an applied load of 150 kgf and is used for harder materials. HRC hardness is typically in the 20–70 range, according to (TechSteel, 2026). The international standard that corresponds to this test is ISO 6508.

Brinell hardness number (HB, HBW)

The Brinell test consists of pressing a large sphere into the metal being tested and measuring the width of the indentation. It is commonly used for castings or forgings because the large impression averages out variations caused by coarse grains. However, it is not suitable for very hard metals or very small parts (Xometry, 2025). ISO 6506.

Vickers hardness (HV)

The Vickers test measures the hardness of a material using a diamond pyramid and different loads, from 10 gf to 50 kgf (Infinita Lab, 2026). The diagonals are measured under a microscope after the test. It is a precise test but requires an optical system and sample preparation; thus, it is more precise but expensive and takes more time than the Rockwell test (Source: ESICT, ca. 2023). The Vickers hardness test is performed according to ISO 6507.

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It is as important to read the label correctly as the number.

● 58 on the Rockwell scale, which is a measure of the hardness of steel.

● The metal is 60 on the Rockwell B scale, so it is a softer metal.

● HBW 10/3000 is a Brinell hardness test using a 10 mm carbide ball indenter and a 3,000 kgf force.

● HV 5 Vickers hardness is measured using a 5 kgf load.

Numbers alone, with no context, are incomplete. Without a scale and units of measurement, nothing can be compared with them.

Scaling is required. What hardness scale?

The appropriate scale depends on the material, size and surface of the part, as well as how quickly you need results. The chart provides a side-by-side comparison of the different scales.

By a certain section condition, use this streaming choice.

1. Rockwell C (ASTM E18) is a measure of hardness.

2. Soft metals like aluminum or copper alloys are measured on the Rockwell B scale or, for thicker stock, with the Brinell scale.

3. Brinell hardness testing (ASTM E10) is suitable for castings or forgings with coarse grains.

4. Vickers (ASTM E92 or E384) on thin coatings or very small features.

5. You cannot move a large part of the installed portion: rebound testers.

In this flow, the choice generally does not depend on the name of the metal. It depends on how large a dent can be made in relation to the part. One cannot make too large a dent in a thin sheet or coating and then read it; that gives an incorrect number. Therefore, it depends more on the size than on how hard the metal is.

A Metal Strength Map for an Element in an Outlook

The hardness table is very helpful. It mentions only the name of the scale and the material’s status, along with the universities.

It can be seen in the chart that 6061-T6 appears three times, and it differs from scale to scale. Conditions matter too: T6 is a temper, and the same alloy with another temper will have different numbers. Steel is the same, and cool grades are very rare.

The charts disagree on the location.

ProleanTech lists 6061-T6 as 40 (HRB 60), which matches Rivcut’s HRB 60 (ProleanTech, 2026). The HRC-style figure beyond that is contradictory. Neither Rivcut’s chart nor TechSteel’s chart gives an HRC value for 6061-T6; HRC applies to steels above about 20 HRC. ProleanTech lists lead at HRB 5, and its 304 stainless values differ from Rivcut’s. When two charts differ, trust the one that gives the name of the scale and the condition, and then check the mill cert.

What Is the Procedure for Converting Rockwell Hardness Values to Brinell and Vickers Hardness Values?

Rockwell, Brinell and Vickers hardness conversions are more an art than a science: ASTM E140-12BR19E01 also provides tables specific to each hardness scale for most materials, and the standard itself suggests, “when a conversion is made it should be done with discretion and under controlled conditions” (ASTM International, 2019). LECO, a popular manufacturer of testing equipment, doesn’t beat around the bush on its website: “The truth is: ASTM E140 conversions are virtually useless as there is no such thing as an accurate conversion using ASTM E140” (LECO, circa 2023).

An example of where translation fails.

ASTM E140 Table 1 says 286 BHN converts to 30 HRC. Private tests show that it converts to <28 HRC in at least one duplex stainless steel (Valve Magazine, 2026). That’s a gap of >2 HRC points, or >6% below the stated 30 HRC. With a spec that tight, that error can allow a part that should fail to pass.

The reason depends on the hardness table; E140 tables are used for certain material categories, such as non-austenitic steels, austenitic stainless steel sheets and copper. Using a table for one material on another alloy family can cause errors (Valve Magazine, 2026).

A rule of thumb and instruments

One should convert hardness only within the same material family. To test hardness on any scale, specify that scale on the drawing. The conversion tables in ASTM E140 are considered the standard reference. There are other methods, too, such as the ZwickRoell hardness converter app. This app converts hardness values to the scales in ISO 18265 or ASTM E140, and even to tensile strength.

Are you aware of what the hardness number doesn’t tell you?

How hard a material is isn't enough to find out how strong or tough it is, or how long it lasts. It tells you how well the surface resists a small, local dent.

According to SA Materials, high hardness implies greater brittleness in various materials. For example, metals can bend before they finally break, whereas ceramic materials often break all of a sudden. The tensile strength values given in conversion tables are only estimates, not actual test results. Hence, if strength is crucial, one should perform a tensile test rather than derive tensile strength from hardness numbers.

This is how we can apply it. We should consider hardness a simple test for determining whether we have carried out the heat treatment in the right range. If our reading is 58–62 on the Rockwell C scale, we have carried out the hardening process accurately. However, this fails to tell us whether the hardening process has made our part fragile.

Frequently asked questions

What is the best hardness test, really?

Rockwell B is often used to test aluminum because it uses a steel ball and a 100 kg load, making it suitable for softer metals. Brinell testing should be used for aluminum that is too thick or coarse for Rockwell B. Hardened steel is tested using HRC, which measures hardness. More often than not, 6061-T6 will read 60 HRB or 95 HB (Rivcut, 2026).

Vickers microhardness testing is suitable for different kinds of materials.

For microscopic components like thin sections, coatings, minor parts and tiny areas such as a weld site, one has to use Vickers microhardness testing. The Vickers microhardness indentation will be tiny, like a 10 gf indentation. You need to refer to ASTM E384 for microhardness testing. The Vickers test will be the slowest and most expensive compared with Brinell and Rockwell tests.

What is the least expensive and quickest method?

According to ESICT (ca. 2023), “Rockwell is the fastest and cheapest method for production. It reads the depth directly, so no microscope is required. That is good for checking many hardened steel parts per shift. Vickers requires optical measurement and preparation, so it takes longer and costs more.”

How does heat treatment or tempering change the hardness of a metal?

A metal’s internal structure changes during heat treatment, so the same alloy can read very differently before and after it. Hardening raises the number; annealing lowers it. The same effect happens with aluminum tempers, e.g., T6. Always record the condition next to the number, e.g., 4140 annealed versus 4140 hardened.

HRC is the Rockwell C hardness scale, commonly used to measure the hardness of hardened steel and other hard metals. It uses a diamond cone indenter pressed into the material under a specified load; the result is reported as a number followed by “HRC,” such as 60 HRC. Higher numbers indicate greater hardness.

HRC represents the Rockwell hardness on the C scale, or Rockwell C, which uses a diamond cone and a 150 kgf major load. Normally, it covers the range of 20 to 70 HRC (TechSteel, 2026). For example, D2 tool steel typically has a hardness of 58–64 HRC.

End

The four scales of the Rockwell hardness test method complement each other. The right test to pick from the group depends on the material, the part’s geometry and what the specification calls for. The scale, load and material condition are the three crucial factors that you should confirm before copying any Rockwell number into a drawing or purchase order. If the hardness specification requires a value on a different scale, then you should request a Rockwell test on that scale instead of relying on a Rockwell hardness number conversion chart.