fsutil fsinfo ntfsinfo [DriveLetter]:
Replace [DriveLetter] with your drive letter.
fsutil fsinfo ntfsinfo c:
The line item to pay attention to is:
Bytes Per Cluster
(You can divide the number by 1024 to get it's value in K ... Example: 16384 / 1024 = 16K)
Hope this helps someone discover the answer faster than having to read a forum! :)