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 
).
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
