Now we must define charge in motion: that is how we can measure the movement of charge. What we're interested in is the movement of charge. And for that we need to know the traffic flow of charge, or how much charge is moving through a passage in a given period of time. 

We wanna know how much charge is passing by a given point per unit of time. Think of it as each charge particle is a car traveling down a road and you're at the side of the road counting how many cars or charge particles pass by that point in a given period of time.

And so we define electric current (or 'current' for short) as the flow of charge through any given point. Current is referred to as the time rate of change of charge which is simply the number of charge particles that pass by a given point per unit of time. Its calculated as the change in charge over the change in time.

Calculation of Current

Prefix Chart for useful unit conversions

The unit of measurement for current is the ampere (amp for short and denoted by a capital A). The ampere is coulombs (the unit of electric charge) per time in seconds.

Since currents are usually small, they are normally given in the form of milliamps (one thousandth of an amp or 1/1000 amp) and is abbreviated as mA. The milli means divided by 1000, so 0.001 Amps equals 1 milliamps (1 mA) since 1 / 1000 = 0.001.

So if your charger has a rating of 115 mA, then that is equivalent to 115*1/1000 amps or .115 amps. To covert from amps to mA, divide the current in amps by 1000. To switch back to amps from milliamps, just multiply by 1000.

Up above is a conversion chart for various common prefixes used in electronics. you can see that m is used as the prefix for milli and to get to milli-anything (milli-amps, milli-volts, etc) you simply divide by 1000 (the same a multiplying by .001 with is equal to 1/1000).