What the energy converter does
This tool converts an amount of energy from one unit into all the others: joule (J), kilojoule (kJ), calorie (cal), kilocalorie (kcal), watt-hour (Wh), kilowatt-hour (kWh), BTU and electronvolt (eV). Type a value, pick the source unit, and every other equivalent appears instantly. All of the math runs in your browser, so nothing is uploaded anywhere.
It comes in handy when a nutrition label reads in kcal but your app shows kJ, when your electric bill talks in kWh, when an air-conditioner manual uses BTU, or when a physics problem needs joules expressed in electronvolts.
How to use it
- Type the number in “Value to convert”.
- Choose the source unit (kWh, for example).
- Read the equivalents in the result cards; the source card stays highlighted.
- Hit “Copy” on any card to send that value to your clipboard.
Very large or very small values, such as the electronvolt, are shown in scientific notation (for example, 2.2469e+25).
The formula
Every unit is anchored to a single base unit, the joule (J), the SI unit of energy. Conversion takes two steps: first the source value is turned into joules by multiplying by its factor, then it is divided by the factor of the target unit.
joules = value × source_factor, then target = joules ÷ target_factor
These are the exact factors the tool uses:
| Unit | Symbol | Equals (in joules) |
|---|---|---|
| Joule | J | 1 |
| Kilojoule | kJ | 1000 |
| Calorie | cal | 4.184 |
| Kilocalorie | kcal | 4184 |
| Watt-hour | Wh | 3600 |
| Kilowatt-hour | kWh | 3,600,000 |
| BTU | BTU | 1055.05585 |
| Electronvolt | eV | 1.602176634 × 10⁻¹⁹ |
The calorie used here is the thermochemical calorie (4.184 J), the standard value in nutrition and chemistry.
Worked example
Convert 1 kilowatt-hour (kWh) into everything else. First move to joules: 1 × 3,600,000 = 3,600,000 J. Then divide:
- Joules: 3,600,000 J
- Kilojoules: 3,600,000 ÷ 1000 = 3600 kJ
- Calories: 3,600,000 ÷ 4.184 = 860,420.65 cal
- Kilocalories: 3,600,000 ÷ 4184 = 860.42 kcal
- Watt-hours: 3,600,000 ÷ 3600 = 1000 Wh
- BTU: 3,600,000 ÷ 1055.05585 = 3412.14 BTU
- Electronvolts: 3,600,000 ÷ 1.602176634 × 10⁻¹⁹ = 2.2469 × 10²⁵ eV
So 1 kWh of electricity equals 3412.14 BTU and 860.42 kcal of energy.
Frequently asked questions
How many joules are in a kilocalorie?
A kilocalorie (kcal) equals 4184 joules. Since 1 kcal is 1000 calories and each calorie is 4.184 J, the product is 4184 J. The capital “Calorie” printed on food labels is actually a kilocalorie.
How many calories are in a kWh?
A kilowatt-hour holds 860,420.65 small calories (cal), which is 860.42 kilocalories (kcal). It comes from dividing 3,600,000 J by 4.184.
What is the difference between a calorie and a kilocalorie?
A kilocalorie is 1000 calories. Nutrition almost always uses the kilocalorie, even though many labels write it as “Calorie” or “cal” out of habit. If a food product says “250 cal”, it almost certainly means 250 kcal.
How many BTU are in a kWh?
A kilowatt-hour equals 3412.14 BTU. That is why an air conditioner’s BTU/hour rating maps onto energy use: a 12,000 BTU/h unit moves about 3.5 kWh of thermal energy per hour.
What is the electronvolt used for?
The electronvolt (eV) is a tiny unit used in particle physics and quantum chemistry: it is the energy an electron gains crossing a potential of 1 volt. It equals 1.602176634 × 10⁻¹⁹ J, so everyday energies become enormous numbers when expressed in eV.