The Storm UI that runs on the nimbus server can show you this. If you don't already have that running, checkout these instructions for details on how to run it (should be at the bottom of the page).
If you're trying to do this test in local mode, though, and don't have the UI, I'd recommend you not even bother. Local mode is not really representative of what kind of performance you'll see on a cluster once all your workers have started and are processing tuples.