Energy Converter
Convert energy between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours and BTU, with 1 kWh = 3.6 MJ and food-energy examples.
Results
Result
You might also need
Educational estimates · not financial advice · free, no signup
Formula / how it works
1 Wh = 3,600 J. 1 kWh = 3,600,000 J. 1 kcal = 4,184 J. 1 BTU ≈ 1,055.06 J. Convert the input to joules first, then divide by the target unit's joules.
Detailed guide
What it is, how to use it, how to read the numbers, common mistakes, a worked example, formulas, and FAQs.
What this calculator is
Energy appears in different units depending on the field: joules in physics, kilocalories in food labels, kilowatt-hours on electricity bills and BTU in heating and cooling. This converter moves a value between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours and BTU by converting through joules. The most common mix-up is calories. A food Calorie is a kilocalorie, which is 1,000 small calories, and the two are different by a factor of 1,000 even though labels often drop the capital C. Always check whether a value is in cal or kcal before converting. Energy is also different from power: a watt is a rate, and a watt-hour is an amount.
When to use / who it helps
- You want to understand the energy on an electricity bill in other units.
- You want to convert food energy into kilowatt-hours or joules.
- You are comparing heating fuels in BTU.
- You are doing a physics or chemistry problem.
- You are comparing energy use between devices.
How to use
Steps
- Enter the value.
- Choose the unit you are converting from.
- Choose the target unit.
- Read the result.
- Check carefully whether you chose calorie or kilocalorie.
- Use scientific notation for very large results.
How to interpret results
- 1 kWh equals 3.6 million joules.
- 1 kcal is 4.184 kJ.
- 1 kWh is about 3,412 BTU.
- Large numbers are easier to read in kJ or MJ.
- Energy and power are not the same thing.
Common mistakes & gotchas
- Confusing calories with kilocalories.
- Treating kWh as a unit of power.
- Rounding BTU conversions early.
- Mixing up Wh and kWh.
- Using a different BTU definition without noting it.
Worked example
Worked example — 1 kWh and a 2,000 kcal day
- 1 kWh = 1,000 Wh × 3,600 J = 3,600,000 J.
- In BTU: 3,600,000 ÷ 1,055.06 ≈ 3,412 BTU.
- 2,000 kcal × 4,184 J = 8,368,000 J, or 8,368 kJ.
- In kWh: 8,368,000 ÷ 3,600,000 ≈ 2.32 kWh.
Result: 1 kWh is 3,600,000 J, and 2,000 kcal is about 2.32 kWh.
To load the form's own demo values, tap Try example above the Calculate button.
How to calculate / formula
1 Wh = 3,600 J. 1 kWh = 3,600,000 J. 1 kcal = 4,184 J. 1 BTU ≈ 1,055.06 J. Convert the input to joules first, then divide by the target unit's joules.
Frequently asked questions
How many joules are in a kWh?
3,600,000.
What is the difference between a calorie and a kilocalorie?
A kilocalorie is 1,000 calories; food labels use kilocalories.
How many BTU is a kWh?
About 3,412.
Is a kilowatt the same as a kilowatt-hour?
No. One is power and the other is energy.
Which unit is used for food energy?
Kilocalories or kilojoules, depending on the country.
Why are there different BTU definitions?
Several versions exist based on the water temperature used; the differences are small.