if the reaction is 1:1 (one unit to one unit)
Then the percentage is:

(min : max) * 100

example: 90 units A and 120 units B

(90 : 120) = 0.75
0.75 * 100 = 75%


example: 55 units A and 7 units B

(7: 55) = 0.127
0.127 * 100 = 12.7%