Q. How can I check the amount that I can shrink a volume from the command line?

A. The Diskpart tool was the original tool used to shrink volumes, and it can still shrink volumes and tell you how much a volume can be shrunk. Just select the disk and partition then use the shrink querymax command, as demonstrated here.

DISKPART> select disk 0

 Disk 0 is now the selected disk.

 DISKPART> list part

 Partition ### Type Size Offset
 ------------- ---------------- ------- -------
 Partition 1 Primary 556 MB 1024 KB
 Partition 2 Primary 118 GB 557 MB
 Partition 3 Primary 113 GB 119 GB

 DISKPART> select part 2

 Partition 2 is now the selected partition.

 DISKPART> shrink querymax

 The maximum number of reclaimable bytes is: 56 GB (57741 MB)