You can find free space of a disk using the below command.
fsutil volume diskfree driveletter
drive letter can be any local drive.
Ex:
C:\>fsutil volume diskfree e:
Total # of free bytes : 45569585152
Total # of bytes : 52427898880
Total # of avail free bytes : 45569585152
Note that this command should be run from elevated command prompt. See How to open elevated command prompt