Logo PTB

Hardness and Tactile Probing Methods

Working group 5.11

Knoop (DIN EN ISO 4545-1)


A diamond indenter in form of a pyramid with rhombic base plane with fixed angles between mutually opposite planes is pressed into the surface of a sample, and the long diagonal d of the indent which remains on the test surface after the test force F has been removed, is measured.

Measurement equation:

F in N, d in mm

Test forces assigned to the hardness scales:

hardness scale Test force, N
HK 0.01 0.09807
HK 0.02 0.1961
HK 0.025 0.2452
HK 0.05 0.4903
HK 0.1 0.9807
HK 0.2 1.961
HK 0.3 2.942
HK 0.5 4.903
HK 1 9.807