Hardness Conversion Calculator

Hardness conversion compares results produced by different indentation or rebound test methods. Rockwell, Brinell, Vickers, Knoop, and Shore instruments do not measure one perfectly interchangeable quantity. They use different indenters, loads, dwell times, optical measurements, and specimen requirements. Published conversion tables are therefore empirical relationships based on tested materials, not exact unit identities. This calculator uses Vickers hardness as an intermediate reference and interpolates representative engineering table values for a practical estimate. Rockwell C is widely used for hardened steels and measures indentation depth under a diamond cone. Rockwell B commonly covers softer metals using a ball indenter. Brinell hardness measures the diameter of an indentation made by a hard ball and is useful for castings and materials with less uniform microstructure. Vickers and Knoop optical methods use diamond indenters and calculate hardness from the resulting impression. Knoop is especially useful for thin layers and brittle materials. Shore D, in contrast, is a durometer scale intended mainly for harder polymers and should be compared with metal scales only with great caution. A conversion can help interpret a supplier certificate, compare historical drawings, select a preliminary machining process, or communicate an approximate requirement when two facilities use different test equipment. It should not replace direct testing when a specification names a required method. Alloy family, heat treatment, work hardening, surface condition, thickness, and test load can all shift the relationship. Two materials with the same Vickers value may not produce identical Rockwell or Brinell readings. Use values inside the normal range of the selected method and treat extrapolated results as rough guidance. The interpolation tables are representative of commonly cited steel relationships, while the Brinell and Knoop links use practical approximations around Vickers. Shore D values are included for broad comparison only because polymer response is strongly viscoelastic and unlike metal indentation behavior. For quality control, aerospace, medical, pressure-equipment, or contractual acceptance work, consult the current ASTM E140 or ISO 18265 tables applicable to the exact material and test conditions. The displayed estimate is most useful for planning and conversation, with the source and target scale kept visible so it cannot be mistaken for a direct measurement.