watt

You probably see "watts" on light bulbs. A watt measures power, which means the rate at which energy is used or produced. A traditional light bulb that gives more light usually needs more watts. It is not just about lights, though; your phone charger, microwave, and even you when exercising all use or produce watts.

Think of water flowing through a pipe: watts are like measuring how fast the water is rushing through. Faster flow means more power. The term honors James Watt, the Scottish inventor who greatly improved the steam engine. He made the idea of "horsepower" popular, and later scientists named this unit after him as a standard way to measure power.

The watt (symbol: W) is the unit of power in the International System of Units (SI). But what exactly is power? It is not energy itself, but rather the rate at which energy is transferred or used. Think of it this way: energy is like a bucket full of water, and power is how quickly you pour that water out.

In technical terms, a watt is defined as one joule per second—meaning one unit of energy is being used every single second.

You'll encounter watts everywhere in electricity. A higher-wattage appliance uses more electrical power. For a long time, light bulbs were rated mainly in watts, and people often used that number as a rough guide to brightness. Today, with efficient bulbs like LEDs, watts tell you more about power use than brightness. Your computer's power supply is also measured in watts, telling you how much power it can deliver to all the internal parts. Even your body uses watts during physical activity; a marathon runner produces far more power than someone reading a book.

Beyond electricity, watts are also used to measure the power of sound (acoustic power) and even the power output of lasers. So, whether you're choosing an energy-efficient light bulb, calculating your electricity bill, or understanding how much effort it takes to climb a flight of stairs, the watt is the fundamental unit for measuring the flow of energy and its rate of use.