Below are lists of the most massive known star clusters in solar masses and sorted in descending order.
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.
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.
| Cluster name | Mass ; (Sun = 1) | Galaxy | Notes | |
|---|---|---|---|---|
| NGC 1569-B | NGC 1569 | |||
| NGC 1569-A | NGC 1569 | |||
| RMC 136 | Large Magellanic Cloud | Contains the most massive known star R136a1 at . | ||
| NGC 346 | Small Magellanic Cloud | |||
| Ara Cluster (Westerlund 1) | 4.45.7 × | Milky Way | ||
| Stephenson 2 (RSGC2) | Milky Way | |||
| RSGC1 | Milky Way | |||
| RSGC3 | Milky Way | |||
| NGC 3603 | Milky Way |