how to find default OS block size?

Hi

Can someone please guide me on how to get the default block size for
all unix flavors.
As per my investigation its 512 for all unix flavours other than HP for which it is 1024.However I am not sure on this.
I even tried the df ommand but utt gives the output w.r.t file system created but I need the OS block size.

It would be great if some one could guide me on this.

thanks

Check this thread.