Below are lists of the most massive known star clusters in solar masses (M☉) and sorted in descending order.
Methods for mass estimation
Globular cluster Globular cluster masses can be determined by observing the proper motion of nearby stars influenced by the cluster or by estimating the cluster's relaxation time.
Open clusters The masses of open star clusters can be estimated by measuring the falloff of radial and tangential velocities of surrounding stars at a particular distance.
List
Globular clusters
Open clusters
See also List of largest star clusters
References
External links The young cluster RMC 136a European Southern Observatory Mayall II Messier Objects Monster Super Star Cluster Discovered In Milky Way ScienceDaily