# Hubble radius

The Hubble radius is the distance from the observer at which the cosmological recession velocity
of a galaxy would equal the speed of light – in mathematical terms, *c*/*H*_{o}, where *c* is the velocity of light and *H*_{o} is the Hubble constant.
Roughly speaking, the Hubble radius is the radius of the observable universe,
and is believed to between about 11 and 15 billion light-years.