Fact: I bought a frame and crankset from a dude and he threw in a couple spiffy track chains. 1 problem though, they're both way to short, at least 3 links need to be added?

Question: Is there a formula for determining what length chain you need (130mm 3/3242t chainring and a 1/8 16t and 18t cog)?

Question: How did you determine what chain length you needed?