When you say "During Production", are you referring to paste flux+solder used in surface mount, which is the majority of mass production today.
The other method is wave soldering for all through hole parts, though the number of devices mass produced with this method is reducing rapidly, mostly appliance boards and other simple line powered circuits where size isn't an issue.
Trying to get an exact value as milligrams of solder per connection will be near impossible for soldering iron+spool of solder, as each joint can vary greatly.
Simply ask purchasing. There is virtually NO way to calculate it. So just look at actual consumption numbers from purchasing. They know exactly how much/when they buy it.