In physics, mobility is used to describe the relation between drift velocity of electrons or holes in a solid material or electrons/ions in a gas, and an applied electric field. The drift mobility is directly related to the electric field as follows,

,

where μ is the mobility.

In metric units, mobility is normally measured in cm2/Vs. Since mobility is a strong function of impurities in a materials well as temperature, it is difficult to provide any values of mobility here for common materials. Mobility is also different for electrons and holess in a semiconductor.