Reference Table
| Energy Unit | Symbol | Definition | Simplified Definition | Example of Use | Where it Might Be Seen |
|---|---|---|---|---|---|
| Watt | W | A unit of power, measuring the rate of energy transfer (1 joule per second). | How fast energy is being used, like how quickly a light bulb shines. | An incandescent light bulb uses about 60 watts of power when turned on, while the average LED light bulb uses about 10 watts. | Power equations, such as: Power = Energy / time (P = E/t) |
| Kilowatt | kW | Equal to 1,000 watts, used to measure the power of appliances and equipment. | A big number of watts, like a thousand light bulbs shining together. | A heater might use 1 kilowatt (1,000 watts) of power to warm up a room. | Power ratings on appliances |
| Megawatt | MW | Equal to 1,000 kilowatts or 1 million watts, often used for power plants. | Like a million light bulbs shining together – a lot of power! | A big wind turbine might produce 2 MW of power, enough for hundreds of homes. | Power output for large systems, like power plants |
| Gigawatt | GW | Equal to 1,000 megawatts or 1 billion watts, used for large-scale power measurements. | A huge amount of power, like a billion light bulbs at once! | A nuclear plant can generate 1 GW of power, enough to power a whole city. | Energy production reports, large energy systems |
| Joules | J | A unit of energy: the amount of energy transferred by applying a force of one newton over a meter. Potential energy (PE): the energy held by an object of its position or state. Kinetic energy (KE): the form of energy an object possesses due to its motion. | A tiny bit of energy, like pushing a toy car a little bit. Potential energy (PE): stored energy Kinetic energy (KE): the energy of movement. | When you throw a ball, you’re using energy measured in joules. | Physics equations, such as: Work (J) = Force (N) x Distance (m) Gravitational Potential Energy = mass x acceleration of gravity x height (PE = mgh) Gravity = 9.8 m/s2 Kinetic Energy = ½ x mass x velocity2 (KE = ½mv2) |
| Foot-Pound | ft-lb | A unit of work or energy equal to the energy needed to lift one pound, one foot. | The energy to lift something heavy, like a book. | When you lift a box onto a shelf, you’re using foot-pounds of energy. | Mechanical engineering, work and energy equations. |
| Calorie | cal | A unit of energy, often used in nutrition, equal to the energy needed to raise the temperature of 1 gram of water by 1°C. | The energy your body gets from food, like the energy from a cookie. | When you eat, your body gets calories of energy to keep you moving and thinking. | Food energy labels, chemistry, and biology. |
| Kilocalorie | Kcal (also shown as Cal) | A unit of energy, often used on food labels, equal to 1,000 calories. | Calories that tell you how much energy food gives you. | A slice of pizza might have 300 kilocalories, providing energy to play. | Nutrition labels, biology, and metabolism studies. |
| BTU (British Thermal Unit) | BTU | The amount of heat required to raise the temperature of 1 pound of water by 1°F. | A way to measure heat, like warming up a cup of water. | A heater might use 10,000 BTUs to warm your room. | Heating and cooling systems, HVAC specifications. |
| Therm | none | A unit of heat energy equal to 100,000 BTUs, often used for natural gas. | A big amount of heat energy, enough to heat a house. | Your gas bill might show how many therms you used to heat your home. | Energy bills and natural gas measurements. |
| Horsepower | hp | A unit of power measuring the output of engines; 1 hp is approximately 746 watts. | Shows how strong an engine is, like how fast a car can go. | A car engine might have 200 horsepower, making it go fast. | Engine specifications, automotive and machinery. |
Additional Information on Power vs. Energy
Power: is the rate at which energy is used or transferred. It’s how quickly something can do work or produce energy, measured in watts (W).
Power measures how quickly energy is used or produced at any given moment.
- Example 1: A 1000-watt light bulb uses power at a rate of 100 watts, but it depends on how long you keep it on to measure total energy.
- Example 2: A microwave with a power rating of 800 watts uses energy faster than a 100-watt light bulb, meaning it heats food more quickly.
- Example 3: A car engine might produce 150 horsepower, which tells us how strong the engine is. The higher the horsepower, the more power the engine produces per second.
Energy: is the total amount of work done or heat produced. It’s the “amount” of power used over time, commonly measured in kilowatt-hours (kWh), joules (J) or BTUs.
Energy measures the total amount of power used over a certain period.
- Example: If a 100-watt light bulb stays on for 10 hours, it uses 1 kilowatt-hour of energy (100 watts x 10 hours).