How to tell how much amperage Arduino board gives?

Ok so i'm wondering how you can tell how much current is going through the wires on an Arduino Uno. The voltage for the 2 outputs is given (5v and 3.3v) but not the current. I'm waiting on an ohmmeter but until then i thought i would ask here since i don't want to fry any parts if i can avoid it.

In this case i was to hook up a speaker that uses 3v (and of course it does not show the amperage limit :P ).

The voltage for the 2 outputs is given (5v and 3.3v) but not the current

You can either measure it with a multimeter or you can calculate it by using ohms law and the resistance of what you are trying to drive.

n this case i was to hook up a speaker that uses 3v

You need to know the impedance of the speaker. It is almost certain you will have to add a series resistor to keep the current down to 30mA on a Uno or 15mA on a Due.

here is an interesting vid on youtube regarding the operating current of 328

https://www.youtube.com/watch?v=iMC6eG24S9g#aid=P9_HHmWVHXo