Determining Bet Pot Amount

[PimplyTeen2]

does anyone know how to calculate the bet pot number?

For instance, on Full tilt there is a button that will allow you to "bet pot". For the life of me I cannot figure out how they come up with this number. what is the equation? It seems fairly simple after the flop, but when someone bets and then you hit "bet pot" it gets confusing.

Say the blinds are 20/40 and there is 80 in the pot...bet pot throws out 160

blinds are 25/50 and there is 75 in the pot...bet pot throws out 175

anybody know how that works?

Thanks,