What is a Watt?

Ever wonder how much power your phone charger uses or how much power a portable power station can supply? The answer involves a small but important unit called a watt. Understanding watts can help you choose the right power solution for your devices, appliances, recreational vehicle, or home.

So... What Is a Watt?

A watt (W) is a unit of power. It tells you how quickly a device is using electrical energy or how much electrical power a source can deliver at a given moment.

Imagine electricity as water moving through a hose. Voltage is similar to water pressure, while current is similar to the rate of water flow. Together, voltage and current determine how much electrical power is being delivered.

• More watts mean more power: A device rated at 1,000W requires more power to operate than a device rated at 100W.
• Watt-hours measure energy over time: Watts tell you how much power a device uses at a given moment. Watt-hours tell you how much energy it uses over a period of time.

A Watt Is a Unit of Electrical Power

A watt tells you how much electrical power a device is using or how much power a source can provide.

Electrical devices have different power requirements. A television, light, microwave, refrigerator, air conditioner, and phone charger may all require different amounts of power, measured in watts.

When selecting a power source, its output must be high enough to meet the power requirements of everything you plan to operate at the same time.

Energy Use Is Measured in Watt-Hours

Electrical power is measured in watts, while the total amount of electrical energy used over time is measured in watt-hours (Wh).

The basic formula is:

Watt-Hours (Wh) = Watts (W) × Hours of Use

For example, a 100W device running for two hours uses approximately 200Wh of energy:

100W × 2 Hours = 200Wh

If a refrigerator draws 500W continuously, the power source must provide at least 500W of continuous output. Running it for one hour would consume approximately 500Wh of energy before accounting for conversion losses.

However, refrigerators normally cycle on and off rather than drawing their full rated power continuously. For a more accurate estimate of daily refrigerator energy use, refer to the manufacturer’s kilowatt-hour rating or measure the appliance with an energy meter.

You should also check the refrigerator’s startup or surge requirement because its compressor may briefly require more power when it starts.

Watts, Kilowatts, and Larger Units

Electrical power can be expressed in several units:

• Kilowatt (kW) = 1,000 watts
• Megawatt (MW) = 1,000,000 watts
• Gigawatt (GW) = 1,000,000,000 watts

Electrical energy is often expressed in watt-hours or kilowatt-hours:

• Kilowatt-Hour (kWh) = 1,000 watt-hours

For example, a 1,000W appliance operating for one hour uses approximately 1,000Wh, or 1kWh, of energy.

The Watt Formula: How Watts Work in a Power System

Watts are determined by voltage and amperage. For direct-current devices and simple resistive loads, the basic formula is:

Watts (W) = Volts (V) × Amps (A)

• Voltage: Voltage can be thought of as electrical pressure. In the hose analogy, higher voltage is similar to higher water pressure.
• Amperage: Amperage, also called current, describes the rate at which electric charge flows. In the hose analogy, it is similar to the amount of water passing through the hose each second.

Larger wires can safely carry more current than smaller wires when properly selected and installed. Wire size must be matched to the current, circuit length, voltage, and applicable electrical requirements.

For example, a 12V device drawing 50A would use 600W of power:

12V × 50A = 600W

The formula can also be rearranged:

• Volts = Watts ÷ Amps
• Amps = Watts ÷ Volts

How to Find Your Device's Wattage

Most appliances and electronics have a label that lists their electrical requirements. Look on the back or bottom of the device, near the power cord, or in the owner’s manual.

The label may show a wattage such as “10W,” or it may list voltage and amperage, such as “120V, 5A.”

For direct-current devices, you can generally multiply volts by amps to calculate watts.

For alternating-current devices, multiplying volts by amps provides the apparent power in volt-amperes (VA). The actual power consumption in watts may be lower because of the device’s power factor.

For AC equipment, actual power can be expressed approximately as:

Watts = Volts × Amps × Power Factor

Whenever possible, use the manufacturer’s stated wattage rather than estimating it from voltage and amperage alone.

How to Choose the Right Power Supply

Portable power stations, power banks, generators, and other power systems have output ratings measured in watts. Battery-powered products also have energy-capacity ratings measured in watt-hours.

These ratings answer two different questions:

• Watts: What devices can the power source operate?
• Watt-Hours: Approximately how long can a battery-powered source operate those devices?

Continuous Output

Continuous output is the amount of power a power source can provide during normal operation. The combined running wattage of your devices should remain below this rating.

Surge Output

Some appliances briefly require additional power when they start. Refrigerators, air conditioners, pumps, compressors, and power tools may have startup requirements that are significantly higher than their normal running wattage.

Your power source must have enough surge capacity to handle these brief increases.

Battery Capacity

A battery-powered unit’s watt-hour rating helps estimate how long it can operate a device.

A simplified runtime estimate is:

Estimated Runtime = Usable Battery Capacity in Wh ÷ Device Wattage

For example, a power station with 1,000Wh of usable capacity could theoretically operate a 100W device for approximately 10 hours:

1,000Wh ÷ 100W = 10 Hours

Actual runtime will normally be lower because of inverter losses, temperature, standby consumption, battery-management requirements, and variations in the device’s power use.

General Wattage Examples

The following ranges provide a general starting point. Always check the specific power requirements of your equipment.

• Low Wattage: 1W to 100W — Common for smartphones, tablets, lights, routers, and other small electronics.
• Medium Wattage: 100W to 500W — Common for laptops, televisions, fans, cameras, and some compact appliances.
• High Wattage: 500W and Above — Common for microwaves, refrigerators, coffee makers, power tools, pumps, air conditioners, and other larger appliances.

Some home appliances require several thousand watts, especially when multiple devices are operating simultaneously. Whole-home backup systems may require substantially more power and should be sized according to the home’s electrical loads and the homeowner’s backup priorities.

It is generally wise to choose a power source with some additional output capacity rather than operating continuously at its maximum rating.

Watt's Next?

Understanding watts makes it easier to compare devices, estimate electrical loads, and select an appropriately sized power source.

Remember these three key points:

• Watts measure power.
• Watt-hours measure energy capacity or energy used over time.
• Surge wattage accounts for the brief increase in power some appliances require when starting.

Whether you are charging devices while camping, powering equipment at a remote location, or preparing your home for an outage, understanding these ratings will help you choose a system that can safely and reliably meet your needs.