According to the Wikipedia entry (see related link) Neptune has 13 known moons.
Yes, it's diameter is 30,685 miles, it is also a gas giant.
Netune is and average length of 49,530 diameters. Hope this helps!! :)
the 13 moons are all the same size which is 98729 km, except the giant Triton which is 876589 km.
There are no moons ON Neptune, moons orbit a planet, they do not sit on it.