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Convert energy across joules, kilojoules, calories, kilocalories, kilowatt-hours, BTU, and electron-volts for physics, nutrition, and bills.
Unit
Generated on July 8, 2026
Convert energy across joules, kilojoules, calories, kilocalories, kilowatt-hours, BTU, and electron-volts for physics, nutrition, and bills.
An energy converter moves between units used in physics (joules, electron-volts), nutrition (calories, kilocalories), electricity (kilowatt-hours, BTUs), and engineering. All measure the same physical quantity — the capacity to do work — but at vastly different scales, from the 10⁻¹⁹ joules of one electron-volt to the 3.
Formula
All conversions route through joules (SI base). 1 kcal = 4,184 J. 1 kWh = 3,600,000 J. 1 BTU ≈ 1,055 J.Energy conversions usually arrive in your life through one of three side doors. Door one: your K-Electric or LESCO bill comes in showing units of kWh and you want to know which appliance is eating it — your AC, your geyser, or your old fridge that hums day and night. Door two: you read a nutrition label that says 2,400 kJ per serving and realise you have absolutely no instinct for what that means without converting to kcal (it's 574 — basically a Big Mac). Door three: you're shopping for an AC and the salesman says "this is a 1.5 ton unit" and you need to translate that into the actual cooling power (18,000 BTU/hr, about 5.27 kW) so you can match it to your room size. The unifying truth is that joules, calories, kWh, and BTU all measure the same physical quantity — energy — just at vastly different scales chosen for different applications. The food Calorie (capital C) trips up everyone: it's really a kilocalorie, so a "300 calorie" cookie genuinely contains 300,000 small calories or 1.255 megajoules. Once you internalize the conversion factors, your electricity bill, your nutrition label, and your AC sizing all start speaking the same language.
An energy converter moves between units used in physics (joules, electron-volts), nutrition (calories, kilocalories), electricity (kilowatt-hours, BTUs), and engineering. All measure the same physical quantity — the capacity to do work — but at vastly different scales, from the 10⁻¹⁹ joules of one electron-volt to the 3.6 million joules of one kilowatt-hour. A particularly common source of confusion is the nutrition Calorie (capital C), which is really a kilocalorie (1,000 small calories) — a single food 'Calorie' on a label equals 4,184 joules.
A joule is the energy transferred when 1 newton of force acts through 1 meter. The large differences between these units come from their origins: kilowatt-hours suit household electricity billing (1 kW applied for 1 hour = 3,600 kJ), BTUs fit US/UK heating and air-conditioning ratings (energy to heat 1 lb of water by 1 °F), and kcal fits human nutrition. Electron-volts are tiny because they measure individual particle interactions — 1 J equals 6.24 × 10¹⁸ eV.
Common energy-unit conversions for physics, nutrition, and household electricity.
| Joules (J) | kilocalories (kcal) | kWh | BTU |
|---|---|---|---|
| 1000 | 0.239 | 0.000278 | 0.948 |
| 10000 | 2.39 | 0.00278 | 9.48 |
| 100000 | 23.9 | 0.0278 | 94.8 |
| 1000000 | 239 | 0.278 | 948 |
| 3600000 | 860 | 1 | 3,412 |
| 10000000 | 2,390 | 2.78 | 9,478 |
1 kilocalorie (4,184 J) is the food energy in one small apple — enough to power a 60W bulb for 70 seconds.
1 kWh (3.6 MJ) powers a refrigerator for ~24 hours or charges a smartphone ~100 times.
A 2,000 kcal daily diet is roughly 2.3 kWh — equivalent to running a 100 W bulb continuously for a day.
1 liter of gasoline contains ~33 MJ — the energy to lift a small car to the top of a 30-story building.
One food Calorie (as printed on nutrition labels) equals 4,184 joules — a single M&M candy contains about 4 Calories or 17 kJ.
1 kWh of electricity (a typical hour of air conditioning) equals 3.6 million joules — also equal to running ten 100 W bulbs for one hour.
A daily 2,000 kcal diet delivers 8.37 megajoules of energy — roughly what the average adult body burns in a day.
1 BTU ≈ 1,055 joules — air conditioners are often rated in BTU/hour, where 12,000 BTU/hr equals roughly 3.5 kW of cooling.
The kinetic energy of a 1,500 kg car at 60 km/h is about 208 kJ — equivalent to 50 kcal, or the energy in a single cookie.
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