Now this isn’t the most accurate method out there but it is by far the easiest.
Open up your console and type netstat -an | grep :443 | grep ESTABLISHED | wc -l
or even better, for a running total
watch "netstat -an | grep :443 | grep ESTABLISHED | wc -l"
Just to add one more not without getting too technical
netstat -an | grep :443 | grep -v TIME_WAIT | wc -l
should give you all connections that the local server hasn’t closed, depening on your application, this may be more accurate