Kilowatts vs. Amps: What's the Difference and Why It Matters

Published: February 3, 2025 | By Elizabeth Carter, Home Power Expert

When storms knock out power in your neighborhood, a home generator can keep your lights on, your refrigerator running, and your family comfortable and safe. But choosing the right generator can feel overwhelming if you don't understand the basic terms used to describe them.

Have you ever wondered what the "kW" means in a "22kW Generac generator"? Or why some electricians talk about "amps" when discussing your home's power needs? Understanding these electrical terms isn't just for experts – it's essential knowledge for any homeowner considering a backup power solution.

In this straightforward guide, we'll break down the difference between kilowatts and amps in plain language. We'll explain how these measurements affect your generator choice and help you avoid the common mistake of buying a generator that's either too small for your needs or unnecessarily large for your budget.

By the time you finish reading, you'll have the confidence to choose the perfect generator size for your home – no electrical engineering degree required!

Understanding Power: Kilowatts, Amps, and Volts

Electricity is measured in three key units:

Kilowatts (kW)

Measures total power. A 10kW generator can produce 10,000 watts.

Think of kilowatts as the total work your generator can do, similar to how many appliances it can run at once.

Amperes (Amps)

Measures electrical current—how much electricity is flowing.

Imagine amps as the water flowing through a hose. More appliances require a larger flow of electricity.

Voltage (V)

Measures electrical pressure—how hard electricity is pushed through wires.

Standard U.S. outlets are 120V, while heavy appliances like dryers use 240V.

The Formula for Power

The relationship between kilowatts, amps, and voltage is simple once you understand it. For a 240V system, the formula is:

Amps = (Kilowatts × 1000) ÷ Voltage

For example, if you have a 2.4kW appliance running on a 240V circuit, the required amps are:

(2.4 × 1000) ÷ 240 = 10 amps

In American homes, standard outlets provide 120V, but whole-house generators typically deliver 240V to power heavy-duty appliances efficiently.

Kilowatts vs. Amps: A Visual Guide

This line chart illustrates how amps increase as kilowatts increase in a 240V system. For instance, a 10kW generator delivers roughly 41.67 amps.

As you can see, understanding the scaling of amperage with increasing kilowatts is essential for ensuring your generator and electrical system work in harmony.

Important: Your home's circuit breaker panel is rated in amps. Ensure that your generator's output does not exceed the safe operating limits of your home’s wiring.

Common Appliance Amperage Requirements

The following bar chart shows the typical running and starting amperage for common household appliances on a 240V system. Notice that appliances with motors (such as refrigerators and central AC units) often require significantly more power to start.

This data is crucial when planning your generator size because it highlights the surge in amperage that some appliances demand at startup, which is much higher than their normal running requirements.

Kilowatts to Amps Conversion Table (240V)

Generator Size (kW)	Amps at 240V	Typical Home Application
8 kW	33.3 amps	Small home, essential circuits only
10 kW	41.7 amps	Small to medium home, basic needs
14 kW	58.3 amps	Medium home, most circuits
16 kW	66.7 amps	Medium home with AC
20 kW	83.3 amps	Large home, most applications
22 kW	91.7 amps	Large home with AC and electric appliances
24 kW	100.0 amps	Large home with all circuits powered

Step-by-Step: Picking the Perfect Generator for Your Home

List Your Essentials: Write down all the appliances you must power during an outage, such as your refrigerator, lights, and critical electronics.
Determine Running Watts: Find out how many watts each appliance uses during normal operation.
Consider Starting Watts: Add extra wattage for appliances that require a surge of power to start, like AC units and refrigerators.
Calculate Total Load: Sum the running watts of all essential devices and add the highest starting watt requirement.
Add a Safety Margin: Increase the total by 25% to ensure the generator can handle unexpected surges or future expansions.

Pro Tip: If you're torn between two sizes, opting for a slightly larger generator can save you from future headaches when you add new appliances or if your current devices draw more power than expected.

Real-World Example: The Johnson Family's Home

Consider the Johnson family, who own a 3-bedroom home with central AC. They want a generator that can power the essentials during an outage. Their list includes:

Refrigerator: 750W running / 2,250W starting
Central AC: 3,500W running / 10,500W starting
Sump Pump: 750W running / 2,250W starting
LED Lighting (5 bulbs): 50W total
Router and WiFi: 50W
TV (50-inch): 110W

The Johnson family first adds up the running wattage for the items they expect to use simultaneously:

Refrigerator (750W) + Lights (50W) + WiFi (50W) + TV (110W) = 960W

Then, they include the central AC’s running wattage:

960W + 3,500W = 4,460W

However, since the central AC requires a surge of 10,500W to start, this becomes the dominant factor in sizing their generator.

To ensure safety, they add the running watts (960W) to the AC’s starting watts (10,500W), reaching 11,460W.

Adding a 25% safety margin:

11,460W × 1.25 ≈ 14,325W, or roughly 14.3 kW.

Based on these calculations, the Johnson family opts for a 16 kW generator to ensure they have adequate power even during peak demand.

Common Questions About Generator Sizing

Can I simply buy the largest generator available?

While a larger generator might seem like a safe bet, it can be inefficient and more costly to operate. Oversized generators may use more fuel and run less efficiently when operating far below their capacity.

What happens if my generator is too small?

An undersized generator may overload when appliances with high starting power are turned on, causing it to shut down or even sustain damage. It’s crucial to size your generator with a safety margin to handle unexpected power surges.

Do I need to understand all electrical terminology to choose the right generator?

Not at all. While knowing the basics helps, our Generator Sizing Calculator simplifies the process by doing the calculations for you. Simply select your appliances and let the tool estimate the required generator size.

Ready to Find Your Perfect Generator?

Now that you understand how kilowatts and amps affect generator sizing, it's time to take action.

Try Our Sizing Calculator

Key Takeaways

Kilowatts measure the total power output, while amps indicate the flow of electrical current.
Understanding both measurements is crucial for selecting a generator that meets your home’s needs.
Always account for high startup power requirements of appliances with motors.
Using our Generator Sizing Calculator can simplify the process and ensure accuracy.
Adding a 20-25% safety margin is recommended for handling unexpected surges or future load increases.