What is the formula for pot limit poker games?

Let P = current pot size

Let C = the amount the player needs to call the current bet

Then the Raise Maximum = P + C

In order to make the raise the player would need to put 2*(P + C) into the pot.

For example, if the pot is $100 and I need to put $25 in to call, the maximum bet is $125. To make this bet I need to put $150 in the pot (first cover the call and then make the bet).

The amount is however usually rounded up to the nearest even chip denomination.