[Suicide Junkie]

The supplies used by your engines is the sum of the individual supplies used, multiplied by the number of times you use them (# of sectors moved).

So, a ship with 5 Ion Is (10 supplies used) uses 50 supplies per square.
A ship with 5 Ion IIs (8 supplies used) plus 4 Gravitic Drive Is (9 supplies used) spends 8*5 + 4*9 = 76 supplies per sector moved.
If that ship moves 10 squares in a turn, it has spent 760 supplies.