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Mohs Hardness Scale 
Symbol:  HM 

Devised by Austrian mineralogist Frederick Mohs in 1822, Mohs' Hardness is applied to non-metallic elements and minerals. In this scale, hardness is defined by how well a substance resists scratching by another substance. A scale of 1 to 10 with half-step increments is employed. Members with higher scale numbers will scratch the surface of members in equal or lower scales.

The reference minerals for the ten scales are:

1 2 3 4 5
Talc Gypsum Calcite Flourspar Apatite
  [CaSO4· 2H2O] [CaCO3] [CaF2] [Ca5 (PO4)3 (F, Cl, OH)]
 
6 7 8 9 10
Orthoclase Quartz Topaz Corundum Diamond
[KAlSi3O8] [SiO2] [Al2SiO4 (F, OH)2] [Al2O3] [C]

Common Mohs' testing kits consist of low cost specimens of the 10 minerals in the Mohs' scale (or 9 if the expensive diamond is absent), labeled and stored in a wooden box. Specimens are sometimes in the form of metal rods, each containing a fragment of the reference minerals at its tip.

The Mohs' Hardness for common materials are listed below:

Material HM   Material HM   Material HM
Fingernail 2.5   Copper Penny 3   Chalk 3
Tooth Dentin 3 ~ 4   Tooth Enamel 5   Amalgam 4 ~ 5
Gold 2.5 ~ 3   Knife Blade 5.5   Glass 5.5
Pumice 6   Steel File 6.5   Floor Tile 6.5
Tungsten Carbide 9   Silicon Carbide 9 ~ 10   Boron Carbide 9 ~ 10

Since Mohs' Hardness Scale uses existing common minerals as reference measures, it is convenient to use but does not give a continuous range of measurements. For instance, diamond (10) is 140 times harder than corundum (9), whereas flourspar (4) is only marginally (~10%) harder than calcite (3). As a result, the hardness conversions from this calculator are not exact and should be used for reference purposes only.

Convert   HM       
(suggested range: 1 ~ 10)
  HM   5   approximately*
Hardness
Symbol Amount Name Suggested
Range
HB (3000)  497   Brinell 10 mm Standard 3000 kgf  80~445
HB (500)  >> Brinell 10 mm Standard 500 kgf  89~189
HB (Tungsten 3000)  503   Brinell 10 mm Tungsten 3000 kgf  80~620
HB (Indentation)  2.76 mm   Brinell Indentation  6~2
HK  564   Knoop  97~920
HRA  77   Rockwell A-Scale  59~86
HRB  >> Rockwell B-Scale  41~100
HRC  51   Rockwell C-Scale  19~69
HRD  64   Rockwell D-Scale  39~77
HRF  >> Rockwell F-Scale  88~100
HR-15N  86   Rockwell Superficial 15N  69~94
HR-15T  >> Rockwell Superficial 15T  77~93
HR-30N  70   Rockwell Superficial 30N  41~85
HR-30T  >> Rockwell Superficial 30T  53~82
HR-45N  57   Rockwell Superficial 45N  19~76
HR-45T  >> Rockwell Superficial 45T  28~71
HS  69   Shore Scleroscope  17~97
Approx. TS  1840 MPa   Tensile Strength (Approx.)  390~2450
HV  535   Vickers  20~1800

Legend
<< The hardness value is below the acceptable range of the particular hardness scale.
>> The hardness value is above the acceptable range of the particular hardness scale.
### The hardness value is near the limit (within 15%) of the acceptable range of the particular hardness scale.
* The many hardness tests listed here measure hardness under different experimental conditions (e.g. indenters made in different sizes, shapes, and materials, and applied with different loads) and reduce their data using different formulae. As a result, there is NO direct analytic conversion between hardness measures. Instead, one must correlate test results across the multiple hardness tests.

This calculator is based on hardness data compiled from ASM Metals Reference Book 3rd ed, published by ASM International, and Machinery's Handbook 25th ed, published by Industrial Press. The calculator curve-fits multiple hardness data onto a common polynomial basis and then performs an analytic conversion. The accuracy of the conversion depends on the accuracy of the provided data and the resulting curve-fits, and on the valid ranges spanned by the different hardness tests. Converted hardness values should be used for comparative purposes only.

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