Energy Converter

How to use Energy Converter

1. Enter the energy value.
2. Select the unit it is given in.
3. Read every other unit at once.
4. One food Calorie equals one kilocalorie equals 4,184 joules.
5. One kilowatt-hour is exactly 3.6 megajoules.
6. The electronvolt uses the exact SI value, 1.602176634 × 10⁻¹⁹ J, fixed by definition since 2019.

The calorie on your food label is a kilocalorie

A scientific calorie is the energy to raise one gram of water by one degree — 4.184 joules. A food Calorie, capitalised, is a thousand of those. So a 250-Calorie snack is 250 kcal, or just over a megajoule. European labels sidestep the confusion by printing kilojoules alongside, which is why the same chocolate bar shows both 230 kcal and 962 kJ. When converting, check which calorie you have: an order of magnitude of three separates them.

Energy and power are different quantities

A watt is a rate — one joule per second. A watt-hour is an amount — what a one-watt device consumes in an hour, which is 3,600 joules. Electricity is billed in kilowatt-hours because what you pay for is the amount, not the rate. A 2,000 W kettle running for six minutes uses 0.2 kWh; a 5 W LED bulb left on all day uses 0.12 kWh. Confusing the two is why “kW” and “kWh” get swapped in energy reporting constantly, and the difference is not cosmetic.

A sense of scale

One joule is roughly the energy of dropping an apple a metre. A kilowatt-hour — 3.6 million joules — runs a fridge for a day or boils about ten kettles. A BTU, the unit air conditioning is rated in, is 1,055 joules, so a 12,000 BTU/hour unit is drawing about 3.5 kW of cooling. An electronvolt, at 1.6 × 10⁻¹⁹ joules, is the natural unit for particle physics and semiconductor band gaps; silicon’s is 1.1 eV, which is why solar cells respond to the wavelengths they do.