Server space granularity

[#1]

What is the server space granularity - in other words, how much disk space does a 1-byte object occupy? I've counted my file space using a 512-byte granularity and it comes to some 395M, whereas the 'My Webspace' stats says 510M. How can I count my filespace usage and come to the same answer as the server?
Ta.

[#2]

I believe the netapps use a 4KB Block size.

[#3]

Certainly the CGI servers have storage mounted as UFS with a 4Kb inode size, so I would assume that's the same across the whole NetApp appliance.
B.

[#4]

"Normal" webspace uses different hardware to the CGI space, but yes they are both Netapps. Looking into it further (rather than relying on the fluff on the top of my head) Netapp's underlying filesystem (WAFL) uses 4kb block sizes.