What is the Difference Between an Amp, Volt, and Watt?

Amps, volts, and watts are all ways of measuring different aspects of electricity. An ampere, or amp (A or I, for current), is the amount of current in a circuit, while voltage (V) is the strength of the current as it flows through the circuit, and watts (W) are the total electrical power released by circuit per second. One watt is equal to one volt multiplied by one amp, which can also be expressed as

One common analogy used to illustrate these terms is that of a garden hose. Amps represent the rate of water as it flows through the hose, while volts represent the strength of the flow, and the wattage represents the total amount of water that comes out of the hose per second.

Another closely related measurement is ohms (Ω), which is a unit of electrical resistance. Going back to the garden hose analogy, if the hose has a larger diameter, more water will be able to flow through. A circuit with a high degree of resistance, expressed in ohms, is able to carry fewer amps than one with lower resistance, regardless of the voltage. If a high voltage encounters high resistance, the amount of possible current in the circuit will be very low — not much water will get through a narrow hose, no matter how high the pressure is. People often express the relationship between current and resistance as Ohm's law:

Scientists use all of these measurements when working with electric circuits. In their most basic form, electrical circuits consist of a voltage source with a positive and negative terminal, like a battery; a load; and two wires connecting the two. When a current (A) flows out of the negative terminal of a voltage (V) source, it flows towards the positive one through the wires. If it encounters a load in the middle, like a motor or light bulb, it flows through that, releasing power (W), in the form of light or work. The load also provides resistance (Ω), which makes the current flow more slowly.

Understanding how these terms relate to one another can be useful both for performing basic electrical work and determining whether an existing electrical panel can support another appliance. While watts are changeable, voltage is generally fixed, with the US having a 120-volt standard. An appliance that uses a large amount of current, such as an electric stove, may need to be on a separate circuit with a higher voltage. This is because it requires a higher wattage, meaning that it uses up more current per unit of time than other appliances, so it needs more voltage. Without the higher voltage, it wouldn't run, because it would be starved for the current it needed to be able to operate.

Understanding the relationship between various electrical terms can also help consumers evaluate monthly power bills. Electrical consumption is measured in watts, or watt-hours, and power companies measure and bill consumption in kilowatt-hours, which is the equivalent of using 1000 watts of power for one hour. Many households use hundreds of kilowatt-hours each month.

The number of kilowatts billed to each household is connected to volts and amps. Volts remain constant, but amps change based on the demand for current. When people switch on more appliances or run them for longer periods, they increase the demand for current, which in turn increases total watts consumed. By running fewer appliances or switching to more efficient devices that require less current, people can reduce the number of kilowatts consumed and reduce energy bills.