A Practical Guide to Energy Units

Energy is the capacity to do work, but it's measured in many different units depending on the context.

The Key Distinction: Energy vs. Power

This is a common point of confusion. Think of it like this: Power (e.g., Watt) is the *rate* at which energy is used (like speed), while Energy (e.g., kWh) is the *total amount* of work done (like distance).

The relationship is simple: Energy = Power × Time. This is why your electricity bill is in kilowatt-hours (power × time).

Where Each Unit is Used

Joule (J): The standard unit in science. It's the energy to lift a small apple (100g) one meter.

Calorie (kcal): Used in nutrition. It's the energy to raise 1kg of water by 1°C. (Note: 1 Food Calorie = 1 kcal).

BTU: Used in heating & cooling (HVAC) in the US. It's the energy to raise 1lb of water by 1°F.