Its not that simple. You don't want it too tight so it will heat or bind so it is better to start off on the loose side but firm.
Then the next time you go for a run is the time to adjust it. If it is leaking, then tighten a little and observe. When you get it down to an occasional drip while running you are just right. At this setting it will usually not drip while not running.
On my last boat if i over did the presure on the greaser it tended to slowly push the packing material out of the stern gland into the boat also it split the pipe between the greaser and gland. I think little and often is the answer
Normally when re-packed ..... hand tight + half-turn with spanner ONLY. Just enough to nip the packing into forming around the shaft.
The actual sealing is provided by the grease injected in to lubricate the packing etc.
The greaser should be screwed in till grease exudes around the shaft out of the gland.
Litle and often with the greaser is the answer.
When you find that excessive amounts of grease ae being pumped in, then its time to add another half-turn to the packing gland, if not enough try another ... but basically you are now showing that the packing is getting due for replacement .....
When replaceing ..... use the WHITE wax style, NOT black-grey graphite industrial packing.
( To another postee - If the packing is being forced out the front of the gland when using greaser, then there is something wrong either with the packing or the gland ..... IT is often that the shaft has worn and grooved, allowing the packing to 'free-up')
There is no rocket science with these .... just not too much at once, and plenty as little and often !
and if you want to have nightmares...take the shaft out and have a good look at the stern gland! I did and its now undergoing major modification!...Oh and mine had 12 (yes TWELVE!) coils of packing in it!...and the grease never got anywhere near the packing!