Rockwell Hardness Conversion Calculator

About the Rockwell Hardness Conversion Calculator

The Rockwell Hardness Conversion Calculator converts between the most widely used industrial hardness scales — Rockwell C (HRC), Rockwell B (HRB), Vickers (HV), and Brinell (HB). Based on the approximate conversion relationships published in ASTM E140, This calculator also estimates ultimate tensile strength (UTS) for steels, making it invaluable for material selection and quality control.

Hardness testing is fundamental in metallurgy and manufacturing. Different testing methods suit different materials and applications: Rockwell C is the standard for heat-treated steels and hard alloys, Rockwell B covers softer metals like brass and annealed steel, Vickers provides precise measurements across the widest range of materials, and Brinell excels at testing rough or inhomogeneous surfaces. Converting between these scales is a daily task for engineers, machinists, and quality inspectors.

Because hardness conversions are empirical rather than mathematically exact, this calculator uses interpolated data from standard ASTM tables. The tensile strength estimates apply primarily to carbon and alloy steels. For non-ferrous metals, stainless steels, or specialized alloys, consult material-specific conversion charts for the highest accuracy.

When This Page Helps

Material engineers, machinists, heat-treaters, and quality inspectors frequently encounter hardness values in different scales. A part drawing may specify HRC while the available tester reads HV, or a supplier certificate lists HB while the spec requires HRC. It provides cross-scale conversions with tensile strength estimates, eliminating the need to look up printed ASTM E140 tables.

The visual gauge and application reference table help you quickly assess whether a given hardness is appropriate for the intended use — from soft annealed parts to ultra-hard cutting tools.

How to Use the Inputs

1. Select the hardness scale you are converting from using the dropdown.
2. Enter your measured hardness value in the input field.
3. Use the preset buttons to quickly load common hardness values.
4. View converted values on all other scales in the results grid.
5. Check the estimated tensile strength (for carbon/alloy steels).
6. Review the hardness gauge for a visual sense of where the value falls.
7. Consult the reference table for typical applications at each hardness range.

Example Calculation

Tips & Best Practices

• ASTM E140 tables are specifically for steel — use material-specific data for aluminum, titanium, or copper alloys.
• Always use the scale most appropriate to your material to get the most accurate reading, then convert.
• For hardened steels above HRC 68, only Vickers and Knoop scales provide reliable measurements.
• Surface decarburization can make Rockwell readings lower than the core hardness — test polished cross-sections for accuracy.
• When specifying hardness, always include the scale (e.g., "58 HRC" not just "58 hardness").
• Portable hardness testers (Leeb/rebound) have additional conversion uncertainties — use bench testers for critical measurements.

Understanding Hardness Scales

Hardness is not a single physical property but a complex response to indentation that combines elastic modulus, yield strength, work-hardening behavior, and surface condition. Different hardness tests probe different combinations of these properties, which is why conversions between scales are always approximate. The Rockwell test measures depth under load, Vickers and Knoop measure projected indentation area, and Brinell measures a larger impression for averaging over inhomogeneous microstructures.

ASTM E140 and Conversion Accuracy

ASTM E140 provides the internationally recognized hardness conversion tables for metals. These tables are based on extensive round-robin testing across many laboratories. For carbon and alloy steels in the HRC 20–65 range, the conversions are well-established with typical scatter of ±1–2 HRC points. Outside this range — very soft or very hard materials — conversions become increasingly uncertain and should be used with appropriate caution.

Industrial Applications by Hardness Range

Hardness specifications are critical throughout manufacturing: incoming material inspection (verifying mill certificates), process control during heat treatment, and final inspection of finished parts. Automotive gears typically require HRC 58–62, aircraft fasteners need HRC 39–45, and surgical instruments target HRC 55–60. Understanding these ranges and their scale equivalents helps engineers communicate specifications across international supply chains where different scales may be preferred.

Frequently Asked Questions

• How accurate are Rockwell to Vickers conversions?

  Conversions based on ASTM E140 are approximate. For standard carbon and alloy steels the accuracy is typically ±2 HRC or ±15 HV. For other alloys, accuracy decreases and material-specific data should be used.

• What is the difference between Rockwell C and Rockwell B?

  HRC uses a diamond cone indenter at 150 kgf and measures hard materials (steels HRC 20–70). HRB uses a 1/16-inch ball indenter at 100 kgf and measures softer materials (brass, mild steel, HRB 0–100).

• Can I convert hardness to tensile strength?

  For carbon and alloy steels, approximate correlations exist (e.g., UTS MPa ≈ 3.45 × HV). These do not apply to non-ferrous metals, cast irons, or austenitic stainless steels.

• What does Mohs hardness measure?

  Mohs scale ranks mineral scratch resistance from 1 (talc) to 10 (diamond). It is ordinal and nonlinear, so conversions from Vickers or Rockwell are very rough approximations.

• Why does my HRC reading differ from the chart?

  Actual hardness depends on material composition, microstructure, surface finish, and test conditions. ASTM E140 tables are empirical averages for standard steel grades.

• Which hardness test should I use?

  Use HRC for hardened steel, HRB for softer metals, HV for thin sections or microhardness, and HB for castings and rough surfaces. The choice depends on material, thickness, and required precision.