Minimum number of flow to hit reassembly memcap in worst case

memcap: 256mb
memcap: 1gb
depth: 1mb

what will be minimum number of flows which can hit reassembly memcap for above configuration in worst case?

can we drive a formula for it?

is below calculation right?
500 (flow) * 2 (each flow have 2 sessions) * 1mb (depth) = 1000mb= 1gb