The ampere is a unit of measurement used for electrical current. Current is the flow of electrons that flow through a specific circuit. This information can be very useful in case you are trying to connect a tool or appliance to the network, which is the term used to describe the alternating current that flows directly from the generating station of the electric company to your home.
Steps
Method 1 of 3: Converting Watts to Amps
Step 1. Apply the conversion formula for direct current
Electric current, represented by the letter I, and measured in amps (A), can be obtained by dividing the power in watts (W) by the volts (V) of voltage. This is represented by the following formula:

I_{(TO)} = P_{(W)} / V_{(V)}
Or, more simply: Amps = Watts / Volts
Step 2. Understand the power factor (PF) for AC problems
The power factor is an index that represents the real power used to do work and the apparent power supplied to an alternating current circuit, a value that varies between 0 and 1. Therefore, the power factor is the real power (P) in watts, divided by the apparent power (S) measured in voltamps (VA), or:
FP = P / S
Step 3. Calculate the apparent power to obtain the power factor
The apparent power can be calculated with the formula S = V _{mc} x I _{mc} , in which S is the apparent power in voltamperes (VA), V _{mc} is the quadratic mean and I _{mc} is the current of the root mean square; These last two can be obtained by solving the following formula:
 V _{mc} = V_{beak} / √2 in volts (V)
 I _{beak} = I _{beak} / √2 in amps (A)
Step 4. Use the power factor for single phase alternating current
Single phase current will be represented by I and measured in amps (A), and can be calculated by dividing the actual power (P) measured in watts divided by a power factor (FP) multiplied by the root mean square (MC) measured in volts. This is represented like this:

I_{(TO)} = P_{(W)} / (FP x V_{(V)}
Or, more simply: Amps = Watts / (FP x Volts)
Method 2 of 3: Measure DC Amperage with an Ammeter
Step 1. Make sure your current is continuous
Direct current or direct current is current that flows in only one direction. If the circuit is powered by a battery, the current will be continuous.
In most countries, the electricity provided by the grid is alternate. Alternating current can be converted to direct current, but only by means of a transformer, a rectifier and a filter
Step 2. Determine the path of the electricity
To record the amperage of the circuit, you will need to connect an ammeter to it. Follow the positive and negative ends of the battery and the connecting cables to find the path of the circuit.
Step 3. Check the circuit
If there is a circuit break or the battery has a fault, the ammeter will probably not be able to measure the current in that circuit (or not accurately). You will need to turn on the circuit to see if it works normally.
Step 4. Turn off the circuit
For some simple circuits, this may require removing the battery completely. With stronger batteries there is a risk of electrocution, so make sure the circuit is off. If you are unsure, wear rubber gloves to avoid electric shock.
Step 5. Connect the positive end of the ammeter
The appliance should have two wires: one red and one black. The red wire is the positive (+) end and the black wire is the negative (). Take the wire that comes out of the positive end of the battery and attach the tip to the positive end of the ammeter.
The ammeter will not interrupt the flow of electricity, but as current flows through the device, it will measure it, causing a reading to appear
Step 6. Complete the circuit with the negative end of the ammeter
Take the black () wire from the ammeter and use it to complete the circuit you just broke. Pin the wire to where the wire that you attached to the positive end would connect to its destination in the circuit.
Step 7. Turn on the circuit
This may simply mean reinstalling the stack. When doing so, the device should turn on and the ammeter will record the current in amps (A) or milliamps (mA) for devices with lower current.
Method 3 of 3: Calculate Amperage Using Ohm's Law
Step 1. Familiarize yourself with the concept of Ohm's Law
Ohm's Law is an electrical principle that establishes a relationship between voltage and current in a conductor. This law is represented by the formulas V = I x R, R = V / I, and I = V / R, in which the letters designate the following:
 V = the potential difference between two points
 R = resistance
 I = the current flowing through the resistor
Step 2. Determine the voltage of the circuit
If your circuit uses a 9volt battery, you already have part of the equation. You can find the specific voltage of the battery you are using by examining the battery packaging or by doing a quick internet search.
The most common cylinder batteries (AAA to D) provide approximately 1.5 volts when new
Step 3. Locate the resistors in the circuit
You will need to know what type of resistor or rheostat is part of your circuit, and how much resistance the electricity flowing through it is creating. Since each circuit is different (some simple circuits may not even have rheostats), you will need to examine your circuit and locate the rheostats for that particular case, as well as their resistance in ohms (Ω).
 The wiring through which the electricity flows will also offer resistance. It will probably be a negligible amount, unless the wires are badly made, damaged, or the circuit conducts electricity long distances.
 The resistance formula is as follows: Resistance = (resistivity x length) / area
Step 4. Apply Ohm's Law
Due to the fact that the battery voltage is applied to the entire circuit, to approximate the current in the circuit you will need to divide the total voltage by the resistance of each rheostat, measuring it in ohms (Ω). The result will be the current (I) in amperes (A), obtained by the following calculation:
 (V / R_{1}) + (V / R_{2}) + (V / R_{3}), where V represents the total voltage and R the resistance of the rheostat in ohms.