Nodetool listsnapshots

listsnapshots - Lists all the snapshots along with the size on disk and true size. Dropped tables (column family) will not be part of the listsnapshots.

For example:

nodetool listsnapshots

Snapshot Details:
Snapshot Name  Keyspace   Column Family  True Size   Size on Disk

5487138454987  nba        player_name    0 bytes     308.66 MB
2157384283120  nba        player_team    0 bytes     107.21 MB
4824891793663  nba        player_stats   0 bytes      41.69 MB
Parameter Description
Snapshot Name Name of the snapshot
Keyspace Keyspace name
Column Family Column Family (table) name
True Size Total size of all SSTables which are not backed up to disk
Size on Disk Total size of the snapshot on disk

For example:

There is a single 1TB file in the snapshot directory. If that file also exists in the main column family directory, the size on the disk is 1TB and the true size is 0 because it is already backed up to disk.

Nodetool Reference