Energy Converter

Convert between joules, calories, kilowatt-hours, BTU, and electron volts energy units.

Energy Converter tool

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Example

Input: 1 kilowatt-hour (kWh) to British thermal units (BTU)

Result: 3412.141633 BTU

1 kWh = 3,600,000 J and 1 BTU (IT) = 1,055.05585262 J, so 3,600,000 / 1,055.05585262 = 3,412.141633 BTU.

Common Energy Conversions

FromTo
1 kWh3,600,000 J
1 kWh3,412.141633 BTU
1 kWh860,420.650096 cal
1 BTU1,055.055853 J
1 BTU252.164401 cal
1 cal4.184 J
1,000 cal (1 food Calorie)4,184 J
2,000,000 cal (2,000 food Calories)2.324444 kWh
100,000 BTU (1 therm)29.307107 kWh
1 J6.241509e+18 eV
1 eV1.602177e-19 J

Values from this converter, rounded to 6 decimal places.

  1. Select the energy unit you want to convert from (joules, calories, kWh, BTU, or electron volts).
  2. Enter the energy value in the input field.
  3. Instantly see the equivalent energy expressed in the other four supported units.
  4. Use the results for comparing appliance efficiency, nutrition calculations, or physics problems.
  5. Click copy next to any result to save the converted energy value to your clipboard.

Joules, Calories, kWh and BTU Compared

One kilowatt-hour (kWh) is 3,600,000 joules, or about 3,412 BTU. One calorie is exactly 4.184 joules. This converter switches between joules, calories, kilowatt-hours, British thermal units (BTU) and electron volts.

The calorie is the unit that trips people up. The "Calories" on food labels are kilocalories, each worth 1,000 of the small calories this tool uses. So a 250 Calorie snack is 250,000 calories here, or 1,046,000 joules. The tool uses the thermochemical calorie of exactly 4.184 J. Another version, the IT calorie, is 4.1868 J, which is close enough for most uses.

Home energy is the other common case. Electricity is billed in kWh. Gas is often billed in therms, where 1 therm is 100,000 BTU, or about 29.3 kWh. Putting both in kWh lets you compare prices on a fair basis. To see what an appliance costs to run, try the Power Consumption Calculator.

Joules are the SI unit and turn up in physics and on food labels outside the US. Electron volts are tiny units for single atoms and particles. For a sense of scale, 2,000 food Calories equals about 2.3 kWh. To estimate how many Calories you burn in a day, see the Calorie Calculator.

Formula / How It Works

1 J = 0.239006 cal = 2.7778e-7 kWh = 0.000947817 BTU = 6.242e+18 eV

Sources

Frequently Asked Questions

One calorie is exactly 4.184 joules in the version this tool uses. Food labels are different: a food Calorie is a kilocalorie, or 1,000 calories, which is 4,184 joules. Labels outside the US often list both kcal and kJ, so a 250 kcal snack is about 1,046 kJ.
One kWh is 3,412.14 BTU. A British thermal unit is roughly the heat needed to warm one pound of water by one degree Fahrenheit, which is about 1,055 joules. Heaters and air conditioners in the US are often rated in BTU per hour, so this conversion helps compare them with electric models.
Put both on the same energy unit first. Gas is often billed in therms, and 1 therm is 100,000 BTU, or 29.31 kWh. Divide the price per therm by 29.31 to get a price per kWh of heat. Then compare it with your electricity rate, keeping in mind that furnaces and heat pumps differ in efficiency.
About 2.32 kWh. Food Calories are kilocalories, so 2,000 of them is 2,000,000 calories. Enter that figure as calories to see 2.324444 kWh. In other words, a full day of food holds about as much energy as running a 1,000-watt heater for a little over two hours.
An electron volt (eV) is the energy one electron gains when it moves across one volt. It is exactly 1.602176634 x 10^-19 joules. Physicists use it because joules are far too large for single atoms and particles. For everyday energy, the result in eV will be a very large number.

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