How to Convert HB to the RC Hardness Scale

Written by david gray
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How to Convert HB to the RC Hardness Scale
The HB hardness scale is typically used on pencils. (pencil image by AGphotographer from

The HB hardness number of a material is given by the Brinell Hardness test, which measures the indentation made in the surface of a material by a standard sphere at a certain hardness and weight. The RC hardness number is measured on the Rockwell C scale. This test measures the depth of penetration into a material of a standard probe at a standard force. It is possible to convert between these two scales using a conversion chart.

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  1. 1

    Determine the HB hardness of the object. Many times this is marked on the object in question, or a standard value is known. You can find the common hardness of a material from a number of websites. As an example, steel has a common HB value of approximately 200.

  2. 2

    Open a hardness conversion chart, which is available on many websites. In addition to the Internet, these conversion charts can be found in many material science textbooks and in other general engineering reference sources.

  3. 3

    Find the RC hardness number that corresponds to the HB hardness you wish to convert. Conversion charts generally have parallel rows or columns corresponding to different hardness scales. To convert between the scales, first find the known hardness number in that scale's row or column, then read across to the column (or up or down to the row) for the scale you want to convert to.

    For example, for steel, using the hardness conversion chart from the Carbide Depot, an HB hardness level of 200 corresponds to a Rockwell C hardness of 13.

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