Most-used Rockwell scales
Rockwell Hardness Chart — Quick Reference
Use HRC for harder steels, HRB for softer metals, and HRA for carbides or thin hard material. The complete 15-scale chart is directly below.
| Scale | Common use | Indenter | Total force | Historical guidance range |
|---|---|---|---|---|
| HRCRockwell C | Hardened steels, hard cast iron, titanium, deeper case-hardened steel | Spheroconical diamond | 1471 N 150 kgf |
20–70 HRC |
| HRBRockwell B | Softer steels, copper alloys, aluminum alloys, malleable iron | 1.588 mm 1/16 in ball |
980.7 N 100 kgf |
20–100 HRB |
| HRARockwell A | Cemented carbides, thin steel, shallow case-hardened steel | Spheroconical diamond | 588.4 N 60 kgf |
20–88 HRA |
Important: Rockwell scales are different test configurations, not interchangeable units. The ranges above are historical NIST guidance ranges, not acceptance limits.
Complete engineering reference
Full Rockwell Hardness Scale Chart
Scale scope checked against ISO 6508-1:2023; configuration and guidance data adapted from NIST SP 960-5.
Important before comparing scales
Rockwell scales are different test configurations, not interchangeable units. Select the scale using the governing material or product specification, specimen geometry and thickness, expected hardness, and the current test standard.
Search the complete reference: try HRC, HRB, aluminum, hardened steel, diamond, thin, or another application. On smaller screens the Scale column and headers remain visible while the table scrolls.
No Rockwell scale matches these filters. Clear one or more filters or search by scale, indenter, or application.
Scroll horizontally to view additional columns and vertically to view additional rows. Column headers and the Scale column remain visible while scrolling.
| Test configuration | Applied forces | Practical guidance range |
Typical applications | Copy | ||||
|---|---|---|---|---|---|---|---|---|
| Indenter | Ball diameter | |||||||
| HRA | Regular | Spheroconical diamond | —Not applicable | 98.07 N (10 kgf) | 588.4 N (60 kgf) | 20–88 HRA | Cemented carbides, thin steel, and shallow case-hardened steel. | |
| HRB | Regular | Ball | 1.588 mm (1/16 in) | 98.07 N (10 kgf) | 980.7 N (100 kgf) | 20–100 HRB | Copper alloys, soft steels, aluminum alloys, and malleable iron. | |
| HRC | Regular | Spheroconical diamond | —Not applicable | 98.07 N (10 kgf) | 1471 N (150 kgf) | 20–70 HRC | Steel, hard cast irons, pearlitic malleable iron, titanium, and deep case-hardened steel. | |
| HRD | Regular | Spheroconical diamond | —Not applicable | 98.07 N (10 kgf) | 980.7 N (100 kgf) | 40–77 HRD | Thin steel, medium case-hardened steel, and pearlitic malleable iron. | |
| HRE | Regular | Ball | 3.175 mm (1/8 in) | 98.07 N (10 kgf) | 980.7 N (100 kgf) | 70–100 HRE | Cast iron, aluminum and magnesium alloys, and bearing metals. | |
| HRF | Regular | Ball | 1.588 mm (1/16 in) | 98.07 N (10 kgf) | 588.4 N (60 kgf) | 60–100 HRF | Annealed copper alloys and thin, soft sheet metals. | |
| HRG | Regular | Ball | 1.588 mm (1/16 in) | 98.07 N (10 kgf) | 1471 N (150 kgf) | 30–94 HRG | Malleable irons, copper-nickel-zinc alloys, and copper-nickel alloys. | |
| HRH | Regular | Ball | 3.175 mm (1/8 in) | 98.07 N (10 kgf) | 588.4 N (60 kgf) | 80–100 HRH | Aluminum, zinc, and lead. | |
| HRK | Regular | Ball | 3.175 mm (1/8 in) | 98.07 N (10 kgf) | 1471 N (150 kgf) | 40–100 HRK | Bearing metals and other very soft or thin materials, subject to anvil-effect limits. | |
| HR15N | Superficial | Spheroconical diamond | —Not applicable | 29.42 N (3 kgf) | 147.1 N (15 kgf) | 70–94 HR15N | Applications similar to HRA, HRC, and HRD where thinner material or shallower case depth requires lighter forces. | |
| HR30N | Superficial | Spheroconical diamond | —Not applicable | 29.42 N (3 kgf) | 294.2 N (30 kgf) | 42–86 HR30N | Applications similar to HRA, HRC, and HRD where thinner material or shallower case depth requires lighter forces. | |
| HR45N | Superficial | Spheroconical diamond | —Not applicable | 29.42 N (3 kgf) | 441.3 N (45 kgf) | 20–77 HR45N | Applications similar to HRA, HRC, and HRD where thinner material or shallower case depth requires lighter forces. | |
| HR15T | Superficial | Ball | 1.588 mm (1/16 in) | 29.42 N (3 kgf) | 147.1 N (15 kgf) | 67–93 HR15T | Applications similar to HRB, HRF, and HRG for thinner-gauge material. | |
| HR30T | Superficial | Ball | 1.588 mm (1/16 in) | 29.42 N (3 kgf) | 294.2 N (30 kgf) | 29–82 HR30T | Applications similar to HRB, HRF, and HRG for thinner-gauge material. | |
| HR45T | Superficial | Ball | 1.588 mm (1/16 in) | 29.42 N (3 kgf) | 441.3 N (45 kgf) | 1–72 HR45T | Applications similar to HRB, HRF, and HRG for thinner-gauge material. | |
Guidance ranges are historical ISO ranges reported in NIST SP 960-5 and are not acceptance limits. HRA measurements above 88 and HRB measurements below 20 are sometimes encountered; use the current governing test method and product specification.
Download options
Download the currently visible rows from this original NIST-derived scale-reference dataset. The file excludes ASTM E140 conversion values and equations.
Decision aid
Which Rockwell Scale Should I Review?
Use this as a fast starting point when a specification has not already named the scale. Final scale selection still depends on the governing standard, expected hardness, specimen thickness, case depth, geometry, support, and surface condition.
HRC is commonly associated with hardened steels and uses a spheroconical diamond at 1471 N (150 kgf) total force.
Regular scales
Use a 98.07 N (10 kgf) preliminary force with total forces of 588.4, 980.7, or 1471 N. HRA, HRB, and HRC are the most familiar regular scales.
N superficial scales
Use a diamond indenter with a 29.42 N (3 kgf) preliminary force. Review them for harder or case-hardened material when lighter forces are needed.
T superficial scales
Use a 1.588 mm (1/16 in) ball with the lighter superficial force family. Review them for thinner, softer, or nonferrous material.
Specification first
If the drawing, product specification, or acceptance document names a Rockwell scale, that requirement controls when a valid test can be made. This selector is a navigation aid, not a substitute for ASTM E18, ISO 6508-1, or a product-specific standard.
HRA vs HRB vs HRC
HRA
Uses a spheroconical diamond indenter with a 588.4 N (60 kgf) total force. NIST lists cemented carbides, thin steel, and shallow case-hardened steel as typical applications.
HRB
Uses a 1.588 mm (1/16 in) ball with a 980.7 N (100 kgf) total force. It is commonly associated with copper alloys, softer steels, aluminum alloys, and malleable iron.
HRC
Uses a spheroconical diamond with a 1471 N (150 kgf) total force. It is widely used for hardened steels, hard cast irons, titanium, and deeper case-hardened material.
Rockwell C quick reference
HRC Hardness Reference Landmarks
HRC is the most familiar Rockwell scale for hardened steels. These landmarks are not conversion values or acceptance limits; they help orient a reader within the C-scale range.
NIST maintains a low-range Rockwell C standard reference material near this level.
NIST maintains a medium-range Rockwell C standard reference material near this level.
NIST maintains a high-range Rockwell C standard reference material near this level.
These landmarks are orientation points based on NIST Rockwell C standard reference material levels, not recommended material targets. Use the governing product specification for acceptance.
How the Rockwell test works
- The indenter contacts the prepared specimen and the preliminary force is applied.
- After the preliminary-force dwell, the machine establishes the first depth reference.
- Additional force raises the applied force to the scale’s total-force level.
- The additional force is removed while the preliminary force remains applied.
- The final depth is measured; the permanent depth increase determines the Rockwell number.
Unlike Brinell and Vickers testing, Rockwell testing does not require optical measurement of an indentation area. It uses the difference between two depth readings in the force cycle.
Within the same scale, a smaller permanent depth increase corresponds to a larger Rockwell number.
h is the net depth increase in millimeters. The constants depend on regular versus superficial testing and diamond versus ball indenters, so this relationship is not a cross-scale converter.
Conversion
Rockwell Hardness Conversion
Rockwell conversion is not a universal unit conversion. ASTM E140 provides separate material-specific relationships—for example, HRC and HRB relationships for homogeneous non-austenitic steels—so the material family must be known before a comparison is meaningful.
ASTM E140 includes relationships for homogeneous non-austenitic steels in the Rockwell C range.
ASTM E140 separately covers homogeneous non-austenitic steels in the Rockwell B range.
Nickel alloys, cartridge brass, copper, wrought aluminum, white iron, and some stainless-steel products use different relationships.
Use the dedicated calculator to select the source scale, target scale, and applicable material relationship. Converted values remain approximate.
No universal cross-scale equation
Do not interpolate the 15-scale configuration chart below to convert HRC to HRB, HV, HBW, tensile strength, or another property. Use a material-appropriate conversion relationship only when the governing specification permits it.
Worked Rockwell Scale Lookups
Hardened steel specified as HRC
Assumption: The product specification explicitly calls for HRC, and expected values fall within the applicable range.
Lookup: The HRC row shows a spheroconical diamond, 98.07 N (10 kgf) preliminary force, and 1471 N (150 kgf) total force. The historical NIST-reported guidance range is 20–70 HRC.
Interpretation: Those fields identify the configuration to verify. They do not confirm minimum specimen thickness, edge distance, curvature correction, machine verification, or acceptance limits; those checks still come from the current method and product specification.
Thin case-hardened surface
Assumption: The objective is to measure a shallow hardened case, and a regular-scale deformation zone may extend beyond the feature.
Lookup: Filtering to Superficial + Diamond isolates HR15N, HR30N, and HR45N. These use the 29.42 N (3 kgf) preliminary force and total forces of 147.1, 294.2, and 441.3 N.
Interpretation: The N-family is the correct family to examine, but the chart cannot choose among the three loads without expected hardness, case depth, total specimen thickness, geometry, and the governing test requirement.
Sources, Scope, and Dataset Rights
Scale scope checked against ISO 6508-1:2023; configuration and guidance data adapted from NIST SP 960-5 (2001).
The published table is an original 15-row reference assembled from the current ISO public scale scope and the openly reusable NIST guide. The quick lookup and scale-review aid surface those same source-controlled fields; they do not reproduce proprietary ASTM or ISO tables. The NIST guidance ranges are historical context, not current acceptance limits.
- NIST SP 960-5 — Rockwell Hardness Measurement of Metallic MaterialsJanuary 2001. Test principle and reporting: sections 2.2–2.4; configurations and applications: Table 1; scale selection and historical ranges: section 3.1 and Table 2.
- ISO 6508-1:2023 — Metallic materials — Rockwell hardness test — Part 1Edition 5, December 2023. The public abstract establishes the 15-scale scope used here. Proprietary ISO tables and procedures are not reproduced.
- ASTM E18-25 — Rockwell Hardness of Metallic MaterialsCurrent U.S. method scope and public significance-and-use context. Proprietary test tables, annexes, tolerances, and procedures are not reproduced.
- ASTM E140-12B(2019)e1 — Hardness Conversion Tables for MetalsPublic scope supports the material-specific conversion pathways described on this page. No proprietary conversion table, equation, or dataset is reproduced.
- NIST SRM 2810a, 2811a, and 2812a — Rockwell C Scale HardnessProvides low-, medium-, and high-range HRC reference levels used as orientation landmarks in the HRC quick-reference module.
- NIST Open LicenseNIST-authored Technical Series content may be reused with attribution, subject to separately credited third-party material.
Dataset and Source-Check Details
- Dataset
- Rockwell Regular and Superficial Scale Reference — 15 ISO-listed scales
- Publisher
- Turn2Engineering
- Source-controlled fields
- Scale, family, indenter, ball diameter, applied forces, applications, and historical guidance range
- Units
- Force in N with kgf in parentheses; ball diameter in mm with inch fraction
- Known exclusions
- Hardness conversions, tensile-strength estimates, specimen acceptance, and proprietary standard procedures
- Download decision
- Filtered CSV permitted for this NIST-derived scale-reference dataset only
Rockwell Hardness Chart FAQs
HRB uses a 1.588 mm ball and 980.7 N total force, while HRC uses a spheroconical diamond and 1471 N total force. They target different application and hardness ranges, so their numbers are not directly comparable.
A higher number generally indicates greater hardness only within the same Rockwell scale and a valid, comparable testing context. Do not rank bare numbers from different scales.
HRC is common for hardened steels, but the correct scale must be confirmed against the material condition, expected hardness, specimen geometry and thickness, case depth, and governing specification.
Only approximate, material-specific conversions should be used. Alloy, microstructure, heat treatment, and processing affect the relationship, and direct testing on the specified scale is preferred.
No. A Rockwell result is a dimensionless empirical number, but it must always be reported with its scale designation, such as 60 HRC.
Use the Chart as a Configuration Reference
Use the table to identify and compare the named Rockwell configurations, then verify the selected scale, specimen requirements, machine verification, procedure, and acceptance criteria in the current governing standard. Preserve the scale suffix whenever you record, copy, or communicate a result.