Energy Unit Conversion Guide
Energy is measured in many units across different fields — joules in physics, calories in nutrition, kilowatt-hours in electricity billing, BTU in heating and air conditioning, and electron volts in atomic physics. All these units measure the same quantity (energy) and have fixed conversion factors relative to the joule, the SI unit of energy.
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Formula
Energy Converter
Convert energy between Joules, calories, kWh, BTU, and more.
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Worked Example
Given:
Related Calculators
FAQs
What is the difference between a calorie and a Calorie (kilocalorie)?
A small calorie (cal) is the energy to raise 1 g of water by 1°C. A food Calorie (Cal, with capital C) or kilocalorie (kcal) is 1,000 small calories. Nutrition labels use kcal (often written as 'Calories'). When someone says a hamburger has 500 calories, they mean 500 kcal = 500,000 small calories.
What is a BTU?
BTU (British Thermal Unit) is the energy needed to raise 1 pound of water by 1°F. It is widely used in heating, ventilation, and air conditioning (HVAC) in the US. Air conditioner capacity is rated in BTU/hour. 1 BTU = 1,055 joules. A typical UK home might require 30,000–40,000 BTU/hour of heating capacity.
What is a kilowatt-hour in everyday terms?
One kilowatt-hour (kWh) is the energy consumed by a 1,000-watt appliance running for 1 hour. Examples: a 1 kW electric heater runs for 1 hour, a 100 W light bulb runs for 10 hours, a 200 W refrigerator runs for 5 hours. An average UK household uses about 8–10 kWh per day.