What is a Watt?

Graphic of a lightbulb being held up

You may notice that when you buy light bulbs, they typically have a number of watts printed on the box. And, when you pay your utility bill, you can see that your energy usage is measured in kilowatt hours (kWh). The watt is obviously some unit of measurement, but what is the watt, really?

What do watts measure?

Watt is the electrical unit for the rate at which energy is generated or consumed.

One watt is a small amount of power. Power consumption of small devices is typically measured in watts, while power consumption of larger devices is measured in kilowatts (kW). One kW is equal to 1,000 watts.

It's important to note that when buying light bulbs, wattage does not equal brightness. For instance, a 150-watt bulb is not necessarily brighter than a 50-watt bulb. This is especially important when it comes to purchasing energy-efficient bulbs like LEDs. Remember, a watt is the amount of energy consumed, whereas brightness is measured in lumens.

Knowing what a watt measures, though, is only half of the story.

Why do we call it a watt?

All of the credit for the watt’s name goes to the extensive research of the 19th century scientist James Watt. James is best remembered for his major contributions to the invention of the steam engine. Through his research, James worked to develop a different unit of measurement to describe the remarkable force of the steam engine, and ended up also coining the term ‘horsepower’ to measure mechanical power and to help explain the impact of his inventions in more easily understood terms.

Watt calculated that one mill horse (an animal familiar to the people at that time) could move approximately 33,000 pounds of weight the distance of one foot per minute. This assumption of 33,000 foot-pounds per minute became the basis of measuring an object’s power in terms of ‘horsepower.’ Watt’s horsepower measurement was adopted immediately and has withstood the test of time, as it’s still being used today.

As time went on, using watt as an electrical unit of measurement became more common. In fact, when Thomas Edison invented the first reliable light bulb in 1879, the British Science Association (a charity that invests in supporting and strengthening scientific initiatives), determined that James Watt’s namesake was the most suitable unit of measurement.

Watts per horsepower

There’s an interesting connection between horsepower and watts. Mechanical power is basically energy from moving machinery—like a car motor turning the tires. Electrical power can be considered energy from moving electrons, which is essentially the same thing: kinetic energy. And while mechanical power—measured in horsepower—is easy enough to recreate with a mill horse and some weight, electricity is a little trickier to measure with a mill horse. So, how many watts are in a unit of horsepower? Keep reading to find out!

What is a watt equal to?

Here are a few important measurements to know:

  • A ‘kilowatt’ is a unit of power equal to 1,000 watts
  • A ‘kilowatt hour’ describes the amount of energy used to provide 1 kilowatt of power over the course of 1 hour
  • 1 horsepower equals 746 watts Pretty interesting? We think so, too!

As an expert energy supplier with 30 years of experience, we’re happy to answer all of your energy questions - whether they’re about watts, green energy, or home warranty plans. 

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