Energy Converter
This energy converter takes a value in joules and converts it to food calories, kilocalories, kilowatt-hours, British thermal units, and electron volts. It bridges the gap between physics, nutrition, and electrical energy measurement.
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Formula
cal = J ÷ 4.184
The joule is the SI unit of energy. One thermochemical calorie equals 4.184 J. One food Calorie (kcal) equals 4,184 J — note that food labels use 'Calorie' with a capital C to mean kilocalorie. One kilowatt-hour (kWh) equals 3,600,000 J. One BTU equals 1,055.06 J. One electron volt equals 1.602 × 10⁻¹⁹ J.
How to use the Energy Converter
- 1
Enter your energy (joules)
Enter energy in joules to convert to other units.
- 2
Read your results instantly
Results update in real time as you type.
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Energy Units Across Physics, Nutrition, and Engineering
Energy is measured differently depending on the field. Physicists use joules as the SI unit and electron volts for atomic-scale phenomena. Nutritionists use kilocalories (food Calories) to quantify energy in food. Electrical engineers and utility companies use kilowatt-hours for energy consumption. Heating and cooling engineers in the US use BTUs (British thermal units) to rate furnace and air conditioner capacity. When comparing energy across these domains — for example, estimating how many joules of food energy equal one hour of running — this converter provides the translation.
Food Calories vs. Physics Calories
The word 'calorie' causes considerable confusion. In physics and chemistry, a calorie (lowercase) is the energy to raise 1 gram of water by 1°C — 4.184 J. In nutrition, a Calorie (uppercase, or kcal) is 1,000 physical calories, or the energy to raise 1 kilogram of water by 1°C. Food labels always use the kilocalorie, even when they write 'calorie.' A 2,000 Calorie daily diet is actually 2,000 kcal, or 8,368,000 joules. This distinction is critical when doing calculations that mix physics energy units with nutritional data.
Tips & Insights
kWh for Electricity Bills
Your electricity bill charges you per kilowatt-hour. One kWh equals 3.6 million joules. A 1,000-watt microwave running for one hour consumes 1 kWh, which costs roughly $0.10–$0.15 in the US.
BTU for HVAC
Air conditioners and furnaces are rated in BTUs per hour. One BTU/hr equals about 0.293 watts. A 12,000 BTU/hr window AC unit is commonly called a 'one-ton' unit and covers about 550 sq ft.
Electron Volts for Atomic Physics
Electron volts are used for subatomic particle energies. Chemical bond energies are on the order of 1–10 eV. Visible light photons carry about 1.8–3.1 eV. X-ray photons carry thousands of eV (keV). This unit is impractical at human scales but essential in atomic and particle physics.
Worked Examples
Convert 1 kWh to Joules and Calories
3,600,000 J (1 kWh) equals 860,421 calories (cal), 860.4 kcal, 1 kWh, 3,412 BTU, and 2.25 × 10²⁵ eV.
Convert 100 kcal (Food Energy)
418,400 J equals 100,000 cal, 100 kcal, 0.0001162 kWh, 396.6 BTU, and 2.61 × 10²⁴ eV.
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Frequently Asked Questions
What is the difference between a calorie and a Calorie?
A lowercase calorie (cal) is a small unit of energy equal to 4.184 J. A food Calorie (uppercase C, or kcal) is 1,000 calories. Food labels always use kilocalories even when they say 'calorie,' which is why a 'low-calorie' food might contain 100 Calories.
How many joules are in a kilowatt-hour?
One kilowatt-hour equals exactly 3,600,000 joules (3.6 MJ). This is because a kilowatt is 1,000 watts (J/s), and one hour is 3,600 seconds: 1,000 × 3,600 = 3,600,000 J.
What is a BTU used for?
The British thermal unit (BTU) is used in heating, ventilation, and air conditioning (HVAC) in the US. It measures the heat needed to raise 1 pound of water by 1°F. Air conditioner and furnace capacities are rated in BTU per hour.
How do joules relate to newton-meters?
One joule is exactly equal to one newton-meter (N·m). It is the work done when a force of one newton displaces an object by one meter in the direction of the force.
What is an electron volt?
An electron volt (eV) is the energy gained by one electron when accelerated through an electric potential difference of one volt. It equals 1.602 × 10⁻¹⁹ joules and is used in atomic, nuclear, and particle physics.
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