How many amps are needed to weld quarter inch steel?

Well its not only the thikness of steel, but also the size of rod. Using the right size rods it should work with 120 amps.

A good way to tell is if it is stiking a lot, you need more amps. If it is splatering to much or burning holes, then it is to much amps.

Now if you are welding fine, but your rods are heating up 1 or 2 inches up, then you're rods are to small. Also if you don't have enough amps, you can heat the metal with a torch to help.