# Rockwell Hardness Calculator

URL: https://speedycalculator.com/calculators/physics/rockwell-hardness-conversion/
Last updated: 2026-10-30

> The Rockwell hardness calculator converts between a Rockwell hardness number and the permanent indentation depth for regular (A, B, C, D, E, F, G) and superficial (N, T) scales.

## Inputs

- Rockwell scale
- Convert from
- Rockwell hardness number
- Permanent indentation depth h (mm, cm, m, in, µm)

## Results

- Indentation depth
- Rockwell hardness number

## 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
```

## Explanation

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

FieldWhat to enterRockwell scaleChoose one: HRC / HRA / HRD (diamond cone), HRB / HRE / HRF / HRG (ball), Superficial HRN / HRTConvert fromChoose one: Hardness number, Indentation depthRockwell hardness numberA numberPermanent indentation depth hUnits: 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 numberIndentation depth (mm)27.50.14541.250.1175550.0968.750.062582.50.035110-0.02

## 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.

## FAQ

**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).


## Sources

- [MIT OpenCourseWare – Mechanics of Materials](https://ocw.mit.edu/courses/2-001-mechanics-materials-i-fall-2006/)
- [The Engineering ToolBox](https://www.engineeringtoolbox.com/)
- [ASTM E18 – Rockwell hardness of metallic materials](https://www.astm.org/e0018-22.html)