Energy Converter
Convert between energy units used across physics, nutrition, and everyday life — joules, kilojoules, calories, kilocalories (food Calories), watt-hours, kilowatt-hours, BTU, foot-pounds, electronvolts, and ergs.
Results from this calculator are estimates provided for general informational purposes only, based on formulas, rates, and standards commonly accepted as of 2026. Figures may differ slightly from other calculators or professional sources due to rounding methods, differing assumptions, or regional regulations, and rules may change over time. Always consult a qualified professional — such as a financial advisor, healthcare provider, or other relevant specialist — before making decisions based on these results.
Result
1 kcal = 4.184 kJ
1 Kilocalorie = 4.184 Kilojoules
1 Kilojoule = 0.23900574 Kilocalories
1 kcal in every supported unit
What is an Energy Converter?
Energy is the capacity to do work — to move something, heat something, or power something. An energy converter translates a quantity of energy measured in one unit into its equivalent in another, which matters because energy is measured very differently depending on the field: physicists use joules, ergs, and electronvolts; nutritionists and dieters use calories and kilocalories (food Calories); electric utilities bill in kilowatt-hours; and HVAC systems in the US are rated in BTU. All of these describe the exact same underlying physical quantity, just at wildly different scales and historical conventions.
Every unit below is defined relative to the joule, the SI base unit of energy, so any conversion — from a subatomic electronvolt up to a household's daily kilowatt-hour usage — reduces to a single multiplication.
Conversion chart: Kilocalorie to Kilojoules
Conversion table
| Kilocalorie (kcal) | Kilojoule (kJ) |
|---|---|
| 0.01 kcal | 0.04184 kJ |
| 0.1 kcal | 0.4184 kJ |
| 1 kcal | 4.184 kJ |
| 2 kcal | 8.368 kJ |
| 3 kcal | 12.552 kJ |
| 5 kcal | 20.92 kJ |
| 10 kcal | 41.84 kJ |
| 20 kcal | 83.68 kJ |
| 50 kcal | 209.2 kJ |
| 100 kcal | 418.4 kJ |
| 1000 kcal | 4184 kJ |
Supported Units
| Unit | Symbol | In Joules |
|---|---|---|
| Joule | J | 1 J |
| Kilojoule | kJ | 1000 J |
| Calorie | cal | 4.184 J |
| Kilocalorie | kcal | 4184 J |
| Watt-hour | Wh | 3600 J |
| Kilowatt-hour | kWh | 3600000 J |
| British Thermal Unit | BTU | 1055.0559 J |
| Foot-pound | ft·lb | 1.3558179 J |
| Electronvolt | eV | 1.60218E-19 J |
| Erg | erg | 1E-07 J |
About These Parameters
- Value
- The amount of energy you want to convert, expressed in the "From" unit. Accepts decimals — enter a food label's Calorie count, an electricity bill's kWh reading, or any other energy figure.
- From Unit
- The unit your input value is currently measured in — for example, kilocalorie if you're starting from a nutrition label, or kilowatt-hour if you're starting from a power bill.
- To Unit
- The unit you want the result converted into. Use the swap button to flip From and To instantly.
How Energy Conversion Works
The Formula
Every unit here is defined by a fixed multiplier relative to the joule. To convert a value from one unit to another:
result = value × (factor of "From" unit ÷ factor of "To" unit)
For Kilocalorie → Kilojoule: multiply by 4.184. For example, 1 kcal × 4.184 = 4.184 kJ.
Why "Calorie" vs. "calorie" Causes Confusion
The small calorie (cal) is the energy needed to raise one gram of water by one degree Celsius — but the "Calorie" printed on a US nutrition label is actually a kilocalorie (kcal), exactly 1,000 times larger. The convention of capitalizing "Calorie" to mean kilocalorie dates back to 19th-century nutrition science and has stuck ever since, so a food listed as "200 Calories" really contains 200,000 small calories. A typical 2,000 kcal daily diet is equal to 8,368 kilojoules — the figure printed on nutrition labels in most countries outside the US.
From Electronvolts to Kilowatt-hours: The Scale of Energy
Because every unit here reduces to the joule, this converter spans an enormous range of physical scales on a single page — from the electronvolt (about 1.6 x 10⁻¹⁹ J, the energy of a single accelerated electron, used in particle physics) up to the kilowatt-hour (3.6 million J, the energy a typical US household uses in roughly an hour of running several appliances at once, and the unit electricity bills are calculated in). An average American home uses on the order of 28-30 kWh per day, which works out to over 100 billion billion electronvolts — a useful reminder of just how small atomic-scale energies really are.
Example
1 kcal equals 4.184 kJ. For scale, that's about 0× a typical 2,000 kcal daily diet (2,000 kcal, or 2000 kcal).
Frequently Asked Questions
Why is a food Calorie 1,000 times a scientific calorie?
Early nutrition scientists in the late 1800s, including Wilbur Atwater, found the small calorie produced awkwardly large numbers when describing food energy, so they adopted the kilocalorie instead and capitalized it as "Calorie" to distinguish it in writing. The capitalization convention was widely lost in casual use, which is why "200 Calories" on a label actually means 200,000 of the small scientific calories (cal).
How many kWh does an average home use?
A typical US household uses roughly 28-30 kilowatt-hours per day, or around 850-900 kWh per month, though this varies significantly with climate, home size, and appliance efficiency — electric heating, air conditioning, and water heaters are usually the largest contributors.
How accurate are these conversions?
Every conversion factor used here is the exact, internationally defined value (e.g. 1 calorie = exactly 4.184 joules, 1 BTU = exactly 1,055.05585262 joules) — results are limited only by floating-point display precision, not by rounded conversion constants.