Hubble’s Law states that the recessional velocity of a galaxy (V) is equal to the product of the Hubble’s Constant (H) and the distance to that galaxy (D) or V = HD
Hubble’s law is usually expressed as a relationship between redshift and distance.
The exact value of the Hubble constant H is very important in cosmology as it leads to an estimate of the age of the universe helps test theories of Dark Matter and Dark Energy etc. Thus a great deal of effort has gone into working it out.
On 21 March 2013 an European-led research team estimated it to be 67.80 0.77 kilometers per second per megaparsec; this is about 21 km/sec per million light years. What this means is that an object a million light years away would be receding from us at 21 km/sec; an object 10 million light years away at 210 km/sec etc.