So I just replaced the alternator in my 96 Cavalier Z24.

Got the belt back on and got it started, but it was squeeling really bad, and the belt wasn't that tight. So I figure I need to get a new belt.

The problem is I don't know what size belt I need.

1996 Cavalier Z24 with an AEM alternator underdrive pulley.

Please help! I wanna get this finished today and I don't wanna spend all day in the rain!

Thanks,
Shane

A sudden squeeling by the belt after replacing alternator
suggests the belt was installed incorrectly....

First thing to check - belt fits in all the groves in the pulleys,
not one grove off somewhere, slightly twisted ?

If you check and it IS installed properly, you may have just gotten grease or something on it, OR your dead alternator wasn't applying a lot of load to it, OR your battery is run down so the alternator is requiring a lot of juice to charge up your battery... which is incidentally rather bad for your alternator.

1) charge up your battery with a charger to make sure you don't fry the new alt.
2) remove the belt, clean it, and verify it's definitely in the right configuration (although I don't think it's possible to put that belt on wrong and have it work.)
3) if you still think your belt is toast, take it off, and go to the parts store with the belt in hand, and match it up to a belt of the same length in the store.