The behaviour of granular materials such as soils has been well studied on Earth and various models have been proposed to describe this behaviour under a range of conditions, including the application of penetrometry for identifying geotechnical parameters in situ. Properties other than bearing strength such as solid-composition and grain size of these materials are usually determined beforehand by, for example, the use of core samples or sieve analysis. The behaviour of granular materials and the operation of penetrometers in microgravity are much less understood. Core samples and sieve analysis are not available or practical for space missions to small bodies or other planets in the solar system because of mass and power constraints and the mechanical complexity involved. Penetrometers are small, comparatively lightweight instruments suitable as lander payloads. They can be used to study properties of surface regolith such as grain size and penetrometers were a staple payload during the early days of planetary exploration on the Moon, a body with significant gravity. Penetrometers have however never been used on minor bodies and their effectiveness in microgravity is unclear. This work examines to what extent penetrometers can be used to identify grain size distributions in granular samples, both in Earth gravity and microgravity environments. Our penetrometry experiments showed that identification of grain sizes is possible in 1 g, however in microgravity grain size information will require careful post-processing because of high noise levels. We also analysed the effect of penetrometer tip shape and penetration velocity in both gravity regimes. Penetrometers may, with the addition of complementary measurements, be effective tools for constraining regolith grain size below the surface, albeit with some difficulty in microgravity.