This depends on the planet. Some have none, like Venus; some have one, like Earth. Mars has two, Jupiter is a few dozen little ones plus four big ones, Saturn has a bunch. There isn't any single correct answer.
It's rather hard to average this out, as the numbers vary greatly, but here is a list of how many satellites per planet ("moon" is the name of Earth's natural orbital satellite). Mercury - 0 Venus -...
There are 167 known moons around the eight planets of our Solar System. Therefore the average number of moons per planet is 167/8 which gives 20.875 moons. 197 rounded up including Pluto 21 rounded...