Designing and analyzing electrical systems can be challenging as you need to be familiar with many different quantities - watts, volts, amps, coulombs, and ohms to name a few - and how these units relate to each other. In certain systems where the voltage is more or less fixed, such as the wiring of a house or car, watts and amps are sometimes given interchangeably, even though they measure completely different things. For this reason, it is very helpful to learn how to convert watts to amps at a given voltage.
Method 1 of 1: Convert watts to amps
Step 1. Familiarize yourself with the quantities
To understand the relationship between watts and amps, you need to understand three different units: watts, amps, and volts. You could also use the Watts2Amps app, which is available for iPhone, iPod & iPad in the Apple App Store and converts the watts into amperes for you.
Watt is a unit that measures power. Power refers to the rate at which electricity is consumed or generated. For example, when a 100 watt bulb is turned on, it will consume energy at a rate of 1 watt (or 1 joule per second).
Ampere is a unit that measures electrical current. An ampere is defined as 1 coulomb (a unit of electrical charge) that flows per second. More generally speaking, amps refer to the amount of electrons that pass a certain point in a given time.
Volt is a unit that measures electromotive force. The voltage of a given system is the slope of that system that allows electrical current to flow.
Step 2. Learn the formula that relates the 3 quantities to each other
Watts, amps and volts are related to each other in a simple formula. If you divide the power consumption by the voltage, you get the amperage: amps = watts / volts. This formula makes it easy to determine the amperage of a system with a given voltage and current consumption.
Step 3. Determine the voltage of your system
To convert watts to amps, you need to know the voltage of the electrical system you are analyzing. For example, in American households the voltage is 120V, while in Europe and most of Asia it is 230V. If the electrical system you are analyzing is battery powered, the voltage will be on the battery. Car batteries are usually 12 V and small batteries for portable devices are 1.5 V.
Step 4. Divide the power consumption by the voltage to get the amperage
If you know the power consumption and voltage of your system, you can use the formula above to find the power consumption. For example, if the power consumption is 120 W and the voltage is 120 V, then the current is: (120/120) or 1 ampere. This means that in a system with 120 volts, a power of 120 watts corresponds to a current of 1 ampere.