Use this:
https://play.google.com/store/apps/details?id=com.abmantis.galaxychargingcurrent.free&hl=en
It's specifically made for Galaxy phones. Basically shows you 3 lines: The top one or reference is how much current your phone should be getting from an original charger, the second is the maximum current you're getting from your charger, and 3rd is the average current you got over time time you started charging.
Basically, if you're charging via USB connection on PC, it should charge at 460mah, which is really slow and depending on what you're doing with the phone, it may not charge at all. Anything below that and you have a phone that's eating current and not charging.