While it's not possible to "convert" watts to amperes, you can still calculate amperes using the relationship between amperes, watts, and volts. This relationship varies depending on the system (eg AC or DC power), but will always be the same in certain types of circuits. If you're using a fixed-voltage circuit, it's usually common to make a chart that relates watts to amperes for quick reference.
Method 1 of 3: Converting Watts to Amps at Fixed Voltage
Step 1. Find the Watts to Ampere table
For special applications, such as home or vehicle wiring, there are special voltage values. Since these values are always the same, you can create a chart that relates the Watt value to Ampere. This chart is based on equations that relate Watts, Amps, and voltages in all circuits. If you want to use this table, please look it up on the internet. Just make sure you use a table where the fixed voltage values are correct.
- For example, a house typically uses 120V AC (in the US) and a car typically uses 12V DC.
- You can use an ampere calculator to make conversion easier.
Step 2. Find the power value (in Watts) you want to change
If you already have the chart, take a look to find the values you're looking for. These charts usually have multiple rows and columns. There will be a column labeled “Power” or “Watts”. Start there and find the exact value of the power in the circuit you want to measure.
Step 3. Find the amount of electric current (in amperes) that matches the power you are looking for
When you find the Watt measure in the Power column, follow the same row in the “Current” or “Amp” column. The table may consist of several columns. So make sure you read the column labels and get the correct values. Once you've found the amp column, double-check the value to make sure it's in your Watts row of values.
Method 2 of 3: Calculating Ampere Using Watts and DC Voltage
Step 1. Find out the power of the circuit
Look for the label on the circuit you are working on. Power is measured in Watts. This value measures the amount of energy used or created in a certain period of time. For example, 1 Watt = 1 Joule/1 second. This value is needed to calculate the current measured in amperes (or amps).
Step 2. Find out the voltage
Voltage is the electrical potential of the circuit and should also be listed in the table along with the power. Voltage is created because one side of the circuit is electron-rich, while the other side is electron-poor. This causes an electric field (voltage) to be created between the two points. Voltage causes an electric current to flow in an attempt to release the voltage (equalizing the electric charge from one side to the other). You need to know the magnitude of the voltage to calculate the current, or amperage.
Step 3. Prepare the equation
For DC circuits, the equation is very simple. Watts are equal to amperes times volts. Thus, you can find amperes by dividing Watts by volts.
Ampere = Watt/Volt
Step 4. Find the current
Once you have your equation set up, you can calculate the amperage. Do the division to find the amount of amperage. Check the units to make sure the result is in coulombs per second. 1 Amp = 1 Coulomb / 1 second.
The coulomb is the SI (International Standard) unit of electric charge and is defined as the amount of electric charge moving in one second by a constant current of 1 Amp
Method 3 of 3: Calculating Ampere Using Single Phase AC Watts and Voltage
Step 1. Know the power factor
The in-circuit power factor is the ratio of the original power to the apparent power delivered to the system. The apparent power is always greater than or equal to the original power. Therefore, the power factor will have a value between 0 and 1. Look for the power factor listed on the circuit label.
Step 2. Use the single-phase equation
The equation for single-phase AC power related to volts, amperes, and watts is similar to the equation for DC power. The difference is in the use of the power factor.
Amp = Watts / (PF X Volts) and power factor (power factor or PF) is a value without units
Step 3. Find the current value
If you've entered values for watts, volts, and power factor, you'll find the amperage value. We recommend that you find the value for Coulombs per second. Otherwise, the equation is wrong and your calculations will have to be repeated.
To complete 3 phase AC power has more variables than single phase. You must determine whether to use line to line or line to neutral voltages to calculate 3-phase amperage
- Use a calculator.
- Understand that you are calculating amperes from the Watt value and the voltage. You can't "convert" Watts to amperes because the two units measure two completely different things.