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Energy Converter

Food labels carry two numbers for one bar — 200 kcal and 836 kJ — and your electricity bill adds a third in kilowatt-hours, while an air-conditioner spec sheet quotes a fourth in BTU. They are all energy, merely scaled for different industries, which is why arguments about whether a snack is '400 calories' never end. This converter translates any of them into all the others at once.

Enter values

Measured in the unit you select as the from unit

Kilocalories and kilojoules for food labels, kWh for electricity

Results update as you type.

Results

In kilojoules (kJ)
8,368
In kilowatt-hours (kWh)
2.3244
In calories (cal)
2,000,000
In watt-hours (Wh)
2,324.44
In joules (J)
8,368,000
Exact factor
1 kcal = 4.184 kJ

How is the Energy Converter calculated?

Enter the energy and pick the unit printed on the label, bill or spec sheet. The calculator answers in the unit you selected and repeats the amount in kilojoules, kilowatt-hours, calories, watt-hours and joules. The factor row (1 kcal = 4.184 kJ) exposes the exact multiplier, so you can check the packaging yourself next time without opening this page.

Formula

Convert through joules: J = value × from factor, then target = J ÷ to factor. Exact factors: 1 cal = 4.184 J · 1 kcal (the food Calorie) = 4,184 J = 4.184 kJ · 1 Wh = 3,600 J · 1 kWh = 3.6 MJ · 1 BTU = 1,055.05585262 J. A watt is one joule per second, which is the bridge between the electrical and nutritional scales.

Example

A 2,000 kcal diet is 2,000 × 4.184 = 8,368 kJ, the figure printed on labels in the EU and Australia. A 100 W bulb running 10 hours draws 1,000 Wh = 1 kWh = exactly 3,600,000 J, which is the 'unit' on a power bill. Heat one litre of water from 20 °C to 30 °C and it absorbs about 41.84 kJ, or 0.0116 kWh.

Things to remember

The conversions are exact, yet labels still mislead: a food Calorie with a capital C is a kilocalorie, so '100 calories' on a US wrapper means 100 kcal = 418.4 kJ. Check the capitalisation and the unit on the package, feed both through this converter, and the arithmetic will finally agree with your tracking app.

Frequently Asked Questions

What is the difference between calories and kilojoules?

Only the scale — the energy is identical. One food Calorie is a kilocalorie worth 4.184 kJ, so a 600 kcal meal is 2,510.4 kJ. Multiply kcal by 4.184 for kilojoules, or divide kJ by 4.184 to get back to kcal.

How many joules are in a kilowatt-hour?

3,600,000. A kilowatt is 1,000 joules per second running for 3,600 seconds, so 1 kWh equals 3.6 MJ. A 2,000 W heater left on for one hour therefore consumes exactly 2 kWh, which is 7.2 million joules.

Are food calories the same as physics calories?

Not quite — nutrition Calories are kilocalories, a thousand times bigger. A 250 Cal snack is 250 kcal or 1,046 kJ, whereas one small physics calorie is just 4.184 J. Always check whether the label's C is capitalised before comparing.

What is a BTU and where will I encounter one?

A British thermal unit is the energy needed to heat one pound of water by 1 °F, defined as 1,055.05585262 J. Air conditioners rate capacity in BTU per hour, so a 12,000 BTU unit moves about 3.52 kW of heat — the figure to compare with a kW rating.

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