Energy Converter
Convert joules, kilojoules, calories, kilocalories, watt-hours and kilowatt-hours.
The energy converter converts between the units used for food energy, electricity and physics. Food labels often show kcal and kJ together, and electricity bills use kilowatt-hours, so it helps to move between them confidently.
How to use the converter
- Enter the energy value.
- Choose the from and to units.
- See the result and the full table.
- Use kcal for food and kWh for electricity billing.
How the conversion works
Result = value in joules ÷ factor of the target unit
Worked example
1 kilocalorie (food Cal) in other units
1 kcal = 4,184 joules = 4.184 kilojoules
The same energy is 1.163 watt-hours or 0.001163 kWh.
Popular conversions
Jump straight to a single conversion, or use the converter above for any pair.
Who should use this energy converter
- Anyone reading food labels where both kilocalories and kilojoules are printed, and wondering which number to track.
- Households and businesses checking electricity consumption, where the bill is charged per kilowatt-hour.
- Fitness enthusiasts comparing calories burned on a machine with calories eaten.
- Students converting between joules, calories and watt-hours for physics or engineering problems.
Common mistakes to avoid
- Confusing calories with Calories. A food Calorie with a capital C is a kilocalorie — 1,000 small calories. That is why a 100-calorie snack is actually 100 kilocalories, or 418,400 joules.
- Using the wrong conversion between kcal and kJ. One kilocalorie is 4.184 kilojoules, not 4. Rounding it to 4 makes a 4.6% difference and quietly shifts every nutrition calculation.
- Mixing power with energy. A kilowatt is a rate; a kilowatt-hour is an amount. Running a 1 kW appliance for one hour uses 1 kWh — the same as a 500 W appliance running for two hours.
- Assuming a calorie burned on a machine equals a calorie eaten. Labels, treadmills and smartwatches estimate differently, and the machine figure is often generous.
- Forgetting the difference between gross and net energy. A power station consumes far more energy than the electricity it delivers; the conversion efficiency is what disappears as heat.
Food calories and electricity units
Two very different worlds use the same words. In nutrition, the unit is the kilocalorie, sometimes written as a Calorie, and one of them equals 4,184 joules. In electricity, the unit is the kilowatt-hour, which is 3.6 million joules — equivalent to about 860 kilocalories.
That relationship is worth knowing as a reality check. One unit of electricity on an Indian bill, one kilowatt-hour, contains roughly the same energy as 860 food Calories — several full meals. It also explains why an electric vehicle is so efficient compared with a combustion engine: converting heat into motion loses most of the energy, while converting electricity into motion loses very little.
Energy units explained
- Joule
- The SI unit of energy. One joule is the energy needed to move an object one metre with a force of one newton.
- Calorie
- The small calorie — the energy needed to raise one gram of water by 1°C. Rarely used outside physics.
- Kilocalorie
- 1,000 small calories, and the same as a food Calorie. Written kcal on labels.
- Watt-hour
- Energy used by one watt running for one hour. A kilowatt-hour is 1,000 of these and is what utilities bill.
- Watt
- A rate of energy use — one joule per second. It measures power, not energy.
Comparing a meal with a workout
The numbers are easier to judge side by side. A 500 kilocalorie meal contains about 2,092 kilojoules. Running five kilometres burns roughly 300 to 350 kilocalories for an average adult, so a single snack can easily match an entire run. A one-kilowatt heater running for an hour uses 1 kWh, which is about 860 kilocalories of energy.
This comparison is useful for expectations. Exercise is excellent for fitness, but it burns fewer calories than most people assume, and food labels make it easy to undo a workout in a few minutes. When the goal is weight, the kitchen carries more of the load than the treadmill — the exercise is there to protect muscle, heart and mood.
Frequently asked questions
What is the difference between a calorie and a kilocalorie?
A food "Calorie" (capital C) is actually a kilocalorie — 1,000 small calories. A banana listed as 100 Calories contains 100 kcal, or 418,400 joules.
How many kilojoules are in a kilocalorie?
One kilocalorie equals 4.184 kilojoules. To convert food energy from kcal to kJ, multiply by 4.184.
What is a kilowatt-hour?
One kWh is the energy used by a 1,000-watt appliance running for one hour, equal to 3.6 million joules. Electricity bills are charged per kWh, commonly called one "unit".