What's the difference between kWh and kW?

It’s easy to get kilowatt (kW) and kilowatt-hours (kWh) mixed up when talking about energy consumption. The main difference between kWh and kW is in what they measure. To put it simply, a kilowatt is a measure of power and a kilowatt-hour is a measure of energy; power is the rate at which something uses energy, and energy is the capacity to do work.

On your energy bill, the kWh measures the amount of energy that an appliance or device needs to run for one hour. Let’s break the definitions down a little further:

Kilowatt

A kilowatt is simply a measure of how much power an electric appliance consumes—it’s ­­1,000 watts to be exact. You can quickly convert watts (W) to kilowatts (kW) by diving your wattage by 1,000:

1,000 W / 1,000 = 1 kW.

Kilowatt-hour

A kilowatt-hour measures the energy an appliance uses in kilowatts per hour. For example, if you clean your floors with a 1,000-watt vacuum cleaner for one hour, you consume 1 kWh of energy.

Your kilowatt-hour consumption factors in how many watts your appliances use and how often you use them. When you see kWh on your monthly energy bill, it’s a measurement of your electric appliances’ wattage and the amount of time you use them.

The difference between kWh and kW, and what you see on your bill, is that kW reflects the rate of electricity you use, and kWh indicates the amount of electricity you use. Let’s go over a few examples of kW vs kWh in the context of low- and high-power appliances to give you a better idea of how these two units affect each other:

• Lower watts: If you are using a 100-watt device, such as a plasma TV, you would have to watch your favorite shows for 10 hours before reaching 1 kWh.
• Higher watts: If you are running a 2,000-watt appliance, such as a clothes dryer, you only need to power it for 30 minutes to reach 1 kWh.

The power you use on a daily basis can quickly add up to 1 kWh if you are frequently using high-wattage appliances in your home. Keep this in mind, as energy companies typically charge for power on a per-kWh basis.

How do you calculate kWh vs. kW?

Knowing the difference between kW and kWh can give you powerful insights to help monitor and manage your electricity consumption. To calculate the kWh of your appliance, estimate the amount of time you use it and write down the appliance’s wattage (generally found on the label). Remember that one kilowatt equals 1,000 watts, so don’t forget to divide your wattage by 1,000 to convert to kilowatts.

Let’s use a 1500W dishwasher you use for two hours per day as an example for calculating kW and kWh on a monthly basis:

1. Divide the wattage by 1,000 to calculate kW: 1500 watts 1,000 = 1.5 kW
2. Multiply the kilowatts by the hours of daily use: 1.5 kW X 2 hours = 3 kWh per day
3. Find the total energy usage for a month (30 days): 3 kWh X 30 days = 90 kWh per month

Now that we know the monthly kWh for this device, let’s estimate the energy costs. Multiply the kWh by your monthly electricity rate. For the sake of this example, we’ll say it’s 13 cents per kWh:

90 kWh X $0.13 per kWh = $11.70 per month

Make a list of appliances that you frequently use and do the same calculations. You can then start to balance your usage by examining which appliances require the most power (kW) and energy (kWh).

How do companies measure my usage?

Utility companies measure your kWh with digital meters right outside of your home where the power line goes into the property. While traditional meters require a utility service to come to your home, newer digital meters have an electronic display that uses a high-frequency signal to send data to the utility companies.

Monitor your electricity kWh.

Now that you have a better understanding of kW versus kWh, and the different uses of electricity, you can take a closer look at your bill and begin to analyze your energy consumption. For a more detailed understanding, consider investing in a home energy monitor. Many monitors available today are wireless and display your home’s energy consumption in an app. Depending on which monitor you choose, you may even be able to turn appliances on and off when you’re away from home using the app.

Lower your energy costs.

You can lower your electricity bill by being energy conscious and following some easy energy-saving practices. Replace incandescent lightbulbs with energy-saving LEDs and get in the habit of turning off the lights whenever you leave a room. Unplug or turn off appliances if you’ll be away from home for a few days, and resist the urge to leave your devices on standby when you don’t need them.

Look into buying smart power bars for parts of your home with several electronic devices (e.g. entertainment center, office). You can set a timer on a smart power bar so that it automatically turns off power to the devices overnight. Some smart power bars also cut power to all devices once you turn a specific device off. For example, you could program a smart power bar to cut power to your sound system and television as soon as you turn your gaming console off.

What appliances are energy-efficient?

Once you know your usage per appliance, you can use this newfound knowledge to invest in energy-efficient home products. Most appliances and electronic devices have energy-efficient options. Look for the yellow ENERGY STAR® symbol on the appliance. ENERGY STAR® appliances are certified as energy-efficient and perform at the same or better level than similar products on the market.

So, when you’re ready to buy that new washer or dryer, be sure to check out the kW and kWh ratings and make some energy-saving adjustments, like washing with cold water and hang-drying your clothes.