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Rockwell Hardness Scales Chart: Indenter, Load and Use

Choosing the wrong Rockwell scale gives a number that looks valid but cannot be compared to the specification. This chart shows each scale's indenter and load so you can confirm the right setup before testing.

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Scale	Indenter	Minor load (kgf)	Total load (kgf)	Typical use
HRA	Diamond cone	10	60	Cemented carbides, thin hard steel, shallow case hardened layers
HRB	1/16 in steel ball	10	100	Soft steels, aluminum alloys, copper alloys, malleable iron
HRC	Diamond cone	10	150	Hardened and tempered steels, tool steel, deep case hardening
HRD	Diamond cone	10	100	Thin hardened steel, medium case hardened parts
HRE	1/8 in steel ball	10	100	Cast iron, aluminum and magnesium alloys, bearing metals
HRF	1/16 in steel ball	10	60	Annealed copper alloys, thin soft sheet metal
HRG	1/16 in steel ball	10	150	Phosphor bronze, beryllium copper, malleable iron
HRH	1/8 in steel ball	10	60	Aluminum, zinc, lead
HRK	1/8 in steel ball	10	150	Bearing metals and other very soft or thin materials
HRL	1/4 in steel ball	10	60	Plastics and soft bearing metals
HRM	1/4 in steel ball	10	100	Plastics and soft bearing metals
HRP	1/4 in steel ball	10	150	Plastics and soft bearing metals
HRR	1/2 in steel ball	10	60	Plastics and very soft materials
HRS	1/2 in steel ball	10	100	Plastics and very soft materials
HRV	1/2 in steel ball	10	150	Plastics and very soft materials

Loads are the regular Rockwell scales. Superficial scales (15N, 30N, 45N and the T scales) use a 3 kgf minor load and are not listed. Always follow ASTM E18 or ISO 6508 and the test method on your purchase order.

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How to pick a scale

Start with what the drawing or material specification states, for example 58 to 62 HRC. If none is given, select the scale by material: C for hardened steel, B for soft steel and many nonferrous alloys, A for carbide or very thin hard sections. Avoid readings at the extreme ends of a scale. Many labs prefer HRC only when results are above about 20 and HRB between roughly 20 and 100, because accuracy falls at the ends.

Method behind the number

A Rockwell test applies a minor load to seat the indenter, then a major load, and then returns to the minor load. The permanent depth difference is converted to a dimensionless number. Total load equals the minor plus the major load. Thin parts need the part thickness to be at least ten times the indentation depth for diamond indenters, otherwise the anvil affects the result or a superficial scale is needed.

Check the tester with certified test blocks near the expected value
Keep indentations at least three diameters apart
Support the part rigidly, especially on curved surfaces
Report the scale with the value, e.g. 60 HRC

Common mistakes

Using HRC on thin sections, ignoring curvature corrections on round parts, and converting between scales or to tensile strength as if the conversion were exact. Conversion tables are approximations for specific materials and should not be used for acceptance unless the specification allows it. Record the tester ID and block verification date in the inspection record.

Frequently Asked Questions

What is the difference between HRB and HRC?

HRB uses a 1/16 inch steel ball and 100 kgf total load for softer materials. HRC uses a diamond cone and 150 kgf total load for hardened steels. They are different scales and the numbers are not interchangeable.

Can I convert HRC to Brinell or tensile strength?

Approximate conversion tables exist for steels, for example in ASTM E140, but they are estimates. Use them for information only unless your specification explicitly permits conversion for acceptance.

Why is a minimum part thickness required?

The deformation zone extends beneath the indentation. If the part is too thin, the supporting anvil influences the result. Thin parts require a lighter load or a superficial Rockwell scale.

How often should the tester be verified?

Verify with certified reference blocks at the start of each shift or testing session, and follow the periodic verification schedule in the standard and your quality system.

If hardness results are tracked on paper or in spreadsheets, Netray can help route them into ERP inspection lots with the scale and limits attached.

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