You need to divide the numer of stakes you get into the total number of stakes allocated for that section of the bounty.

e.g. If you receive 500 stakes and the total number of stakes allocated to that section of the bounty are 50,000 stakes, then 500/50,000 = 0.01. Therefore you get 0.01* the bounty pot.

Because of this, if the bounty allocation for that section is 100,000 tokens, you'll receive 0.01 * 100,000 = 1,000 tokens.

Basically it's not possible to know how much you'll get until the bounty ends, just hope there aren't a huge number of participants.