What size blocks does NFS server write to disk?

I am trying to calculate required IOPS for a fileserver, and to do this I need to know the typical block size. I know that NFS clients can use rsize and wsize to specify how much data is sent over the network. Does the NFS server also use these same values to write the data to the disk, or is there some other way to configure that? I haven't found anything in the man pages.