Molly fish get as big as four and a half inches in length. However, the actual size of your molly fish will depend on their species.
Wild molly fish tend to grow bigger than mollies that live in captivity, so mollies in home aquariums usually only grow up to three or four inches long.
The size of your molly fish will also depend on their species.
While common mollies are generally only three or four inches long, other molly fish species are smaller or even bigger. For example, balloon mollies are tiny and only grow to be three inches inches long, while black sailfin mollies can grow up to seven inches inches in length!