If this were the only cause of the expansion, the distance to a galaxy would be merely the velocity at which a galaxy moves away from us divided by a constant called the Hubble constant. Since this determines the scale of the model, a particular value is unnecessary. The Hubble constant is between 50 and 100 kilometers per second per megaparsec. This value should become better known as the Hubble Space Telescope makes more measurements. However, things are not so simple.
Galaxies have gravitational fields.
If a region is denser than the surrounding area, galaxies should fall into it. Eventually, the dense region will become a cluster of galaxies. In a cluster of galaxies, the central galaxies are on orbits around the center with periods of around a billion years and galaxies farther out may be falling in. In our part of the universe, there is a region known as the Virgo cluster which contains many galaxies. The Virgo cluster contains hundreds of galaxies within a few degrees of its center.