Instruments used to measure the firmness or consistency of a substance.

The earliest qualitative soil penetrometers were sticks, rods, or the fists or digits of the tester. More reliable and quantitative methods are now available, including digital models.

Penetrometers specifically designed for soil are typically round or cone-shaped. These penetrometers are dropped on or pressed against the soil and the depth of the impression is measured. Alternatively, the cone may be driven into the soil and the amount of required force assessed. The results may help determine:

• Whether the ground is suitable for road-building
• The degree of soil compaction
• The moisture in soil on Earth and on other planets
• The characterization of materials that underlie a glacier
• The condition of the soil for professional cricket matches and horse races
• Potential crop yield and tilth
• Elastic, shear, and rupture properties

Digital penetrometers are also used to test the consistency of greases, waxes, bitumens, pastes, creams, food products, cosmetics, and other solid and semi-solid substances.

Penetrometers may also measure the sturdiness of plant leaves or the firmness of apples and other hard fruits. Penetrometers with cones or plungers and needles can use gravity to penetrate food samples. The penetration distance determines the relative tenderness of baked products and gels.