Memory usage for the ngx_http_limit_req_module module (no replies)

Hello,
I'm using the "nxg_http_limit_req" module to limit the service usage.
I've a questions about the "limit_req_zone" directive: how can I set the correct size for the zone?
In docs I see that "One megabyte zone can keep about 16 thousand 64-byte states", how can I know how much memory is necessary for each state? Is the state a request in the "leaky bucket"?

Regards

Luca