Some examples of supply usage

The higher value is if the units don’t have any ammo stored when you get resupplied. They will have shoots left when the next resupply comes though.

3 mortars can use 1720-2170 supply in 7:30 minutes
15 supply for every shoot * ((7:30min/12 seconds reloadtime)+1)
1 Mortar can store 15*10=150 supplies worth of ammo.

The leig support cannon and pack howitzer can use 536-568
8 supply for every shoot * ((7:30min/6.75 seconds reloadtime)+1)

Russian ZiS-3 860-900
10 log for every shot

German howitzer 1435-1540
35 log for every shot

Nebelwerfer 4490-4895
405 for every salvo

Katyusha 11440-12440
1040 for every salvo