What’s the Difference Between Amps and Watts?
Amp up your DIY electrical knowledge
Highlights
Watts and amps are closely related but entirely different measurements.
Volts are necessary in the amp vs. watt relationship.
An amp is a measure of electrical volume.
A watt measures the ability of an electrical system to perform work.
Understanding the difference between various electrical terms, such as amps vs. watts, is helpful when talking with your electrician or figuring out your monthly electrical bill. However, the terminology itself can be the confusing part. You're not alone if you've ever wondered why your home's electrical panel has amps written all over it while your electric bill asks for money in exchange for watts or kilowatts.
Defining Amps and Watts
Amps and watts share a close relationship. The amount of amps directly affects an electrical system or circuit's wattage or watt measurement. However, another player in the game, called volts, is a crucial component of the relationship between amps and watts.
Amps
Amps measure the volume of electrical current. Current reflects how many electrons are passing through a wire or system. Your home's electrical panel uses breaker switches that turn themselves off, or trip, for safety when too many amps are trying to get through a single circuit.
You can think of amps as the volume of electricity moving in a wire.
Watts
Watts reflects the total working power of an electrical source. If watts equaled the power of horses and your antique wagon required two horses to pull it, you could say it needs two watts to complete the task. In the scenario, amps could be the number of steps the horses take.
Volts
The pressure that pushes on the amps, and is the missing factor in the equation to determine the watts of a circuit, is volts or voltage. In our horse and wagon story, volts might equal the power of the horses' leg muscles.
How Amps, Volts, and Watts Relate
Watts is simply the sum of amps multiplied by volts. If you have fewer amps, you'll need more volts to equal the same wattage. The same is true the other way around.
Watts is the total number of amps (number of horse steps) multiplied by the volts (horse muscles) that it takes to perform work (pull your wagon to market). However, because electricity (horses) comes in varying strengths and volumes, there are a few ways to tell the wagon story.
The equation is Amps X Volts = Watts or A x V = W.
Suppose your horses didn't eat breakfast today, so they feel sluggish. While it still takes two horses to pull the wagon to market, neither is strong today. Their volts or muscle strength are low. However, if they take more and smaller steps (amps) than usual to get to market, their muscles (volts) won't have to work as hard, but the task is complete when your wagon gets to the market (watts)—the same amount of work gets done by increasing the number of steps while using less force.
On the other hand, if your horses ate a healthy meal and perhaps had a few extra sugar cubes today, they feel strong, like they have extra muscles (volts). With the extra voltage power, they can run with long strides, reducing the number of steps (amps) it takes to get to the market. The journey still requires two horses (watts), but by adding muscle strength (volts), they were able to get there with fewer and longer steps (amps). The total remains at two watts to achieve the result.
Measuring Watts
Determining the wattage of an electrical system, circuit, or device is possible after learning how many volts and amps are present. Determining voltage or amperage requires simply adjusting the equation if you already know the wattage and the volts or amps.
You can determine amps, volts, and watts using a multimeter. Measure watts in a 110V home electrical circuit using an ammeter or the ammeter function on your multimeter to determine the amp measurement. Multiply the house voltage by your recorded amp measurement to reveal the watts.
If your home operates on typical 110V municipal electricity and you want to know the maximum possible watt capacity in one of the house's electrical circuits, look on the circuit's breaker switch for the amp rating. Multiplying the house voltage by the amp rating equals the watts the circuit can handle—sort of. Home electrical circuits shouldn't ever operate at full capacity and generally max out at around 80% of available power.
You can also determine how many amps a light bulb requires to operate. Because amps equal watts divided by volts, a 60W light bulb on a 110V circuit will need roughly half an amp.
If you need to know if a 15A breaker can handle the load of a space heater, find the wattage rating on the device. A 1,500W space heater operating on 110V household electrical will demand 13.6 amps. While a 15A breaker could handle the space heater if it were the only device running on that circuit, you can more easily avoid tripping the breaker if you plug it into a 20A circuit.
When to Use Amps, Volts, and Watts
Understanding what amp, volts, and watts are is only part of the battle. Knowing when to use amps vs. watts vs. volts is essential as well. Here are some examples.
Use amps when talking to your local electrician about how many of what kind of electrical circuits you'd like to add to your house during a breaker panel upgrade.
Use volts to determine compatibility when purchasing a large electrical appliance that may operate on either 110V or 220V residential electrical power.
Use watts when determining the total power available in an electrical circuit, deciding whether to purchase a 1,000 or 1,500-watt space heater or choosing an outlet to plug it into.