The Hubble constant is most frequently quoted in (km / s)/ Mpc, thus giving the speed in km/s of a galaxy 1 megaparsec (3.09 × 10 km) away, and its value is about 70 (km/s)/Mpc. However, crossing out units reveals that H 0 is a unit of frequency (SI unit: s) and the reciprocal of H 0 is known as the Hubble time. The Hubble constant can also be interpreted as the relative rate of expansion. In this form H 0 = 7%/Gyr, meaning that at the current rate of expansion it takes a billion years for an unbound structure to grow by 7%.