The Rockwell test measures how deep an indenter sinks under a major load after a preload. Each 0.002 mm (regular) or 0.001 mm (superficial) of depth is one hardness point. HRC is used for hard steels and HRB for softer metals.
How to use the Rockwell Hardness Calculator
- Rockwell scale
- Convert from
- Rockwell hardness number
- Permanent indentation depth h
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose the scale, then enter either the hardness number or the depth.
Inputs explained
| Field | What to enter |
|---|---|
| Rockwell scale | Choose one: HRC / HRA / HRD (diamond cone), HRB / HRE / HRF / HRG (ball), Superficial HRN / HRT |
| Convert from | Choose one: Hardness number, Indentation depth |
| Rockwell hardness number | A number |
| Permanent indentation depth h | Units: mm, cm, m, in, µm |
Example values
How the main result changes when Rockwell hardness number changes and everything else stays at the example values above:
| Rockwell hardness number | Indentation depth (mm) |
|---|---|
| 27.5 | 0.145 |
| 41.25 | 0.1175 |
| 55 | 0.09 |
| 68.75 | 0.0625 |
| 82.5 | 0.035 |
| 110 | -0.02 |
Formula
Regular diamond scales (A, C, D): HR = 100 − h/0.002 mm · Ball scales (B, E, F, G): HR = 130 − h/0.002 mm
Superficial scales (N, T): HR = 100 − h/0.001 mm
Worked example
Inputs — Rockwell scale: HRC / HRA / HRD (diamond cone); Convert from: Hardness number; Rockwell hardness number: 55.
Results — Indentation depth = 0.09 mm.
Key terms
- Indentation depth
- Permanent depth increase caused by the major load.
Frequently asked questions
What is a typical HRC for a knife?
About 55–62 HRC.
Why do ball scales use 130?
So that soft materials still give positive numbers.
What loads are used?
Preload 10 kgf (3 kgf for superficial scales); major loads 60–150 kgf (regular) or 15–45 kgf (superficial).
Can Rockwell be converted to Brinell or Vickers?
Only approximately, using material-specific tables (ASTM E140).