I am trying to create a simple way to track ammunition for my upcoming sandbox game. In this system, players will buy ammunition in (for lack of a better word) "packets". One packet of ammunition contains enough for one encounter. To work out the price of a packet, all I need to do is multiply the cost of one arrow (or bolt, etc.) with the number of arrows fired in the average combat encounter. I understand that number of arrows used will double when extra attack is gained. I can work around that easily by making players with extra attack spend two packets per encounter.
(Why bother with ammunition at all if I'm going to simplify it this much? Because I also have a simplified encumbrance system, so this ties into that. Players have to decide how many fights' worth of ammunition they are willing to carry.)
However, to be able to work this out, I need to know how long the average encounter is. When I say "average", I mean a medium or hard difficulty encounter in which 4–6 characters face off against a similar number of opponents. In other words, what might be considered the bog-standard, run-of-the-mill encounter.
I would be particularly interested to hear from someone who has been recording the length of each encounter (as unlikely as that may be).