Formula that depends on value within a range
I presume that an order of 20 requires 1 (one) package and an order of 80 requires 4 (four) packages. If those are your numbers, then
=ROUNDUP(order_size/20, 0)should work. So, for example, if the order size is in cell
A1, you would use
=ROUNDUP(A1/20, 0)