Rockwell Hardness Conversion Calculator

Rockwell hardness measures how deeply an indenter penetrates a material under a specified minor and major load. A smaller permanent indentation produces a larger Rockwell number. The letter following HR identifies the indenter and load combination, so HRC, HRB, and HRA are not interchangeable units. HRC is widely used for hardened steels, HRB for softer steels and copper alloys, and HRA for thin or exceptionally hard materials. Other scales extend the method to plastics, bearings, thin sheet, and specialized material ranges. This calculator maps the source reading to an equivalent HRC position and then maps that position onto the selected target scale. The affine anchors reproduce common engineering reference points, such as approximately 40 HRC corresponding to 74 HRA and approximately 20 HRC corresponding to 96 HRB. Selecting the same source and target returns the original reading. Results are rounded to one decimal place because extra displayed precision would imply more certainty than a cross-scale estimate can support. Hardness conversion is inherently approximate. Different Rockwell scales use different indenters, loads, penetration depths, and valid material ranges. The relationship also changes with alloy composition, heat treatment, cold work, surface condition, specimen thickness, and microstructure. Two materials with the same HRC reading can therefore produce somewhat different HRB or HRA readings. Published ASTM E140 tables are based on empirical measurements for named material groups rather than a single universal physical equation. Use converted values for screening, drawing review, specification comparison, or deciding which test scale may be suitable. Do not use an estimate as a substitute for a direct test when accepting production parts, certifying a heat treatment, or resolving a contractual specification. Check that the specimen is thick enough, the surface is prepared correctly, and indentations are spaced according to the applicable test standard. If a conversion falls outside the normal range of either scale, treat it cautiously and test directly. For repeatable results, record the original scale and reading alongside any converted estimate. That preserves traceability and prevents a rounded secondary value from being mistaken for a measured result. When supplier certificates and design drawings use different scales, this converter offers a fast first comparison while clearly retaining the limitations that responsible hardness evaluation requires.