ELECTRICITY BASICS

Watts, Kilowatts, and Kilowatt-Hours

Understand the critical difference between power (watts) and energy (kilowatt-hours), and learn how they determine your monthly utility bill.

2 min read Updated Aug 19, 2026 DataWisdom
Power × Time = Energy
kW × Hours = kWh

In this guide

  • The difference between power and energy
  • What is a watt?
  • What is a kilowatt?
  • What is a kilowatt-hour (kWh)?
  • How to convert between units

A watt is a measure of electrical power (speed), a kilowatt is 1,000 watts, and a kilowatt-hour (kWh) is a measure of total electrical energy consumed over time (distance). You are billed by your utility for kilowatt-hours.

Power versus energy

To understand your electricity bill, you must understand the difference between power and energy. Think of electricity like driving a car:

  • Power (Watts/Kilowatts): This is like your speedometer. It tells you the rate at which you are currently using electricity.
  • Energy (Kilowatt-hours): This is like your odometer. It tracks the total amount of electricity you have consumed over time.

What is a Watt (W)?

The watt is the fundamental unit of electrical power. It indicates how fast an appliance draws electricity. A 10-watt LED bulb draws power very slowly, while a 1,500-watt space heater draws power very quickly.

What is a Kilowatt (kW)?

A kilowatt is simply 1,000 watts. Because household appliances can draw thousands of watts, it is mathematically easier to group them into kilowatts.

To convert watts to kilowatts, divide by 1,000.

  • 1,500 Watts = 1.5 kW
  • 60 Watts = 0.06 kW

What is a Kilowatt-Hour (kWh)?

A kilowatt-hour (kWh) is the unit of energy that your utility company uses to bill you. It represents running a 1,000-watt (1 kW) appliance continuously for exactly one hour.

However, you can reach 1 kWh in many different ways:

  • Running a 1,000W heater for 1 hour (1 kW × 1 hour = 1 kWh)
  • Running a 100W lightbulb for 10 hours (0.1 kW × 10 hours = 1 kWh)
  • Running a 10W LED bulb for 100 hours (0.01 kW × 100 hours = 1 kWh)
Calculate kWh
(Watts ÷ 1,000) × Hours Used

Definitions

  • Watts: The power drawn by the appliance.
  • Hours Used: The duration the appliance is actively drawing power.

Example

A 2,000W oven running for 3 hours uses (2,000 ÷ 1,000) × 3 = 6 kWh.

Worked conversion example

Let's calculate the daily energy use (kWh) and cost for a 1,200-watt microwave that is used for 30 minutes (0.5 hours) every day. The local electricity rate is $0.15 per kWh.

Worked Example
Scenario: A 1,200W microwave operates for 0.5 hours per day at $0.15/kWh.
Illustrative Power to Energy Conversion
Step Calculation Result
1. Convert W to kW 1,200 W ÷ 1,000 1.2 kW (Power)
2. Convert to kWh 1.2 kW × 0.5 hours 0.6 kWh (Energy)
3. Calculate Cost 0.6 kWh × $0.15 $0.09
Takeaway: Despite having a high wattage (power), the short runtime means the actual energy consumed (kWh) is low, costing less than 10 cents per day.
Note: This example assumes the microwave draws 1,200W continuously. Microwave power levels (e.g., 50% power) may pulse the magnetron on and off, changing the calculation.

Limitations

While understanding kWh is essential for estimating appliance usage, your final utility bill will also include fixed delivery charges, taxes, and fees that are not strictly tied to your kWh usage. Your effective rate may be higher than your advertised supply rate.

For more information on our calculations, please read our Methodology and Disclaimer.

How this guide was prepared

This guide was prepared using standard formulas and publicly available utility practices. Examples shown are illustrative and actual rates and bill structures will vary by provider and location. We recommend reviewing your specific utility tariff for exact charges. Learn more about our methodology.

Sources

  1. U.S. Energy Information Administration: Electricity explained
ELECTRICITY BASICS QUESTIONS

Frequently Asked Questions

Find answers about this topic, calculated estimates, and related concepts.

Read our calculation methodology →

WHAT YOU WILL FIND HERE

  • Direct explanations
  • Short illustrative calculations
  • Links to relevant calculators and guides
What is the difference between kW and kWh?
kW (kilowatt) is a measure of power, indicating the rate at which electricity is being used at a specific moment. kWh (kilowatt-hour) is a measure of energy, indicating the total amount of electricity consumed over a period of time.
How many watts are in a kilowatt?
There are 1,000 watts in one kilowatt (kW).
What am I billed for: watts or kilowatt-hours?
Utility companies bill residential customers for energy consumed, which is measured in kilowatt-hours (kWh).
How do I calculate kWh from watts?
Divide the watts by 1,000 to get kilowatts, then multiply by the number of hours the device was turned on.
Looking for a question that is not covered here? Contact DataWisdom.
NEXT STEP

Convert Watts to Cost

Now that you understand the difference between watts and kWh, use our calculator to estimate exactly how much your devices cost to operate.

Calculate Electricity Cost Read Your Utility Bill

Related Calculators

Electricity Cost Calculator

Convert wattage and runtime into cost.

Appliance Energy Cost

Calculate specific appliance costs.

Continue Learning

Basics

Understanding Your Electricity Bill

Learn how to read an electricity bill.

8 min read
Appliances

How to Calculate Appliance Costs

Convert wattage to actual utility costs.

6 min read