The Ultimate Guide to Watts vs. Amps

Understanding the difference between watts and amps will help you safely navigate electrical projects. Most people's basic understanding of electricity tells them that voltage refers to how powerful a circuit is, but this isn't entirely accurate or representative of the whole picture. If you don't understand volts vs watts vs amps, you can't understand how much power a circuit is producing.

Below, we've explained the difference between wattage and amperage to help you better understand power supplies and demands for electric appliances and devices.

What Is Amperage?

Amperage refers to an electrical circuit's number of Amperes, often simply called "amps." Amps are a value used to measure electrical current, which is the volume of electricity moving through a circuit.

While voltage determines how much initial pressure of electrons is put on the circuit, the amperage determines the volume of those electrons that are flowing through the circuit.

To put this into practical terms, a 120-volt circuit with a 10-amp current has the same volume of electrons as a 240-volt circuit with a 5-amp circuit, even though the voltage of the 240-volt circuit is double that of the 120.

This is why many experts say you should be more concerned with amps than volts when trying to avoid electrical shock.

Warning

Regardless of the voltage or amperage, always consider an electrical circuit to be potentially dangerous. When working around electrical components, remove or disable the power source beforehand and use an electrical tester to confirm that the power is off before continuing.

The Importance of Amperage

Amperage is so important because it determines the actual power of a circuit, whereas the voltage simply determines the potential power of the circuit. The current is limited by another electrical value called resistance, which is measured in ohms.

Imagine pouring a 5-gallon bucket of water into a funnel. While you may fit the entire five gallons in the top of the funnel, it will still exit the tapered bottom of the funnel at a slow, steady rate. However, if you were to cut off the bottom of the funnel and make the exit hole larger, the water would flow out much faster. This is because you decrease the resistance.

This is exactly what happens when you lower the resistance of an electrical circuit. As you lower resistance, you increase the electrical flow (current) without having to increase the initial electrical pressure (voltage).

Battery Charger Amp Selection

One tangible example of amperage you've likely come across is varying current options on a battery charger, such as for a 12-volt car battery. These options typically look like 2 amp, 4 amp, or 6 amp, and are present on a charger to allow you to charge the battery at slower or more rapid speeds.

Selecting higher amps on the charger increases the rate of power delivery to the battery, which results in a quick charge while selecting lower amps on the charger results in a slow charge. Some chargers even have a "maintain charge" option, which uses a very small amount of current to simply keep a battery from dying while sitting.

What Is Wattage?

Wattage is the rate of power flowing from the circuit. One "watt" is equal to one unit of energy being transferred per second. In plain terms, watts are the rate at which the electrical energy is supplied or utilized.

To reference the amperage example above, both the 120-volt circuit with a 10-amp current and the 240-volt circuit with a 5-amp current produce 1200 watts of power. So, independently increasing either variable (volts or amps) in a circuit will increase the wattage of the circuit.

The Importance of Wattage

So, why is wattage important? Appliances and devices have a specified electrical demand that must be met for them to function properly and safely. If the power supply cannot meet these demands, the device can break or pose a safety risk. This is why wattage is so important and why you must connect an electrical device to a circuit that can meet its power demands.

A 3,000-watt electric stove can't be plugged into a 120-volt circuit with 10 amps of current, as this produces less than half of the power needed to meet its watt requirements. Instead, the stove must be plugged into a 240-volt circuit with 15 amps of current, which has a power capacity of 3,600 watts.

Tip

The importance of understanding wattage goes beyond simply meeting the power demands of one electric appliance or device. What happens when you power multiple appliances and devices on the same circuit, as we often do in our homes every day? Trying to power too many things at once on a given circuit can overload the circuit, which will trip a breaker or blow a fuse.

Light Bulb Wattage Options

One everyday example of wattage you'll see is light bulb wattage. A 60-watt incandescent light bulb uses more energy than a 40-watt incandescent light bulb.

The 60-watt bulb powered by a standard 120-volt outlet should use 120 volts of power at 500 milliamps (.5 amps), because 120 (volts) x .5 (amps) = 60 (watts). The 40-watt light bulb plugged into the same outlet will use roughly only 333 milliamps or .333 amps. The resulting lower power draw results in the light being dimmer.

The difference in wattage between the light bulbs is a result of the lower-watt light bulb having higher resistance than the higher-watt light bulb. As explained above, the higher the resistance, the lower the current. The lower current results in a lower power draw.

Warning

Using a light bulb with higher wattage than accepted by the fixture can damage the fixture and pose a safety risk.

How to Calculate Watts and Amps

Use the following formulas to find electrical values like watts and amps:

• To find a circuit's wattage using its amperage and voltage, use this formula: amps x volts = watts

• To find a circuit's amperage using its wattage and voltage, use this formula: watts/volts = amps

• To find a circuit's voltage using its amperage and wattage, use this formula: watts/amps = volts

Frequently Asked Questions

How many watts are in an amp?

There is no set number of watts in an amp, as the number is determined by the circuit's voltage. A 12-volt circuit with a 10-amp current produces 120 watts, but a 120-volt circuit with the same 10-amp current produces 1,200 watts. In this example, the voltage is what manipulates the wattage.

What is the difference between a watt and an amp?

An amp is a measure of electrical current or the volume of electrons moving through a circuit. A watt is what you get when you multiply an amp times a volt, which is the pressure of electrons on a circuit. So, a watt is the resulting power supply of the circuit when considering both the amps and the volts.

Does higher amps mean more power?

On the same voltage, higher amps means more power. For instance, a 120-volt circuit with a 5-amp current produces 600 watts of power, while a 10-amp current on the same circuit produces 1,200 watts of power.

Read Next: Understanding Electrical Current Flow in Circuits

Read the original article on The Spruce.