What version of Apache are you running? It all depends how it's threaded on whether that command would work ...
You should probably just use mod_status to show a nice status page which will be more accurate than the above methods. If you don't know how to, do a Google and you should find a site that explains it.
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to expand on dans (and mine previously) reply - apache can use threads, which look like a single process (and in fact are), but in reality each process can hold a whole pile of threads which will each hold a new client connection
maybe a better ps command would be ps -efL|grep apache (its the NLWP column) and count the threads..