Durometer is one of several ways to indicate the hardness of a material, defined as the material's resistance to permanent indentation. The term durometer is often used to refer to the measurement, as well as the instrument itself. Durometer is typically used as a measure of hardness in polymers, elastomers and rubbers. There are several scales of durometer, used for materials with different properties. The two most common scales, using slightly different measurement systems, are the A and D scales. The A scale is for softer plastics, while the D scale is for harder ones.

Durometers are designed to measure the indentation hardness of materials such as hard rubber, plastics and epoxies. Durometers are used with a test stand or as hand-held testers. Durometers come standard with an ancillary hand for indicating peak readings.