Energy Converter
Joules, kWh, kilocalories, BTU and electronvolts for bills, food labels and physics
Joules, kWh, kilocalories, BTU and electronvolts for bills, food labels and physics. No data leaves your browser – every conversion happens locally.
Energy units you'll actually meet
The joule is the base unit. Electricity bills use kilowatt-hours (3.6 million joules each), food labels use kilocalories (4,184 J), air conditioners and heaters in the US quote BTU (about 1,055 J) and physicists use electronvolts for single particles.
This tool converts energy, not power. Watts, horsepower and BTU per hour measure how fast energy is used, so a "1.5-ton" AC rated at 18,000 BTU/h can't be converted here directly. Multiply power by running time first to get energy.
Common energy conversions
| 1 kWh → J | 3,600,000 J |
| 1 calorie | 4.184 J |
| 1 kcal | 4,184 J |
| 1 BTU | 1,055 J |
| 1 kWh → kcal | 860 kcal |
Good to know
Calories on food labels are kilocalories
When a food label says '200 calories', it means 200 kcal (kilocalories) = 200,000 small calories. The small calorie (4.184 J) is used in chemistry. The food calorie is always the kilocalorie.
Worked examples
A daily diet
2,000 kcal is 8,368 kJ, or about 2.32 kWh. That's roughly what a 100 W bulb uses in a full day.
Monthly electricity
A 300 kWh bill is 1,080 megajoules. Gas bills in some countries are quoted in MJ, so this lets you compare the two.
Phone battery
A 15 Wh phone battery holds 54 kJ, about the same energy as 13 kcal of food.
One amount of energy, five ways
Each row shows the same energy in joules, kilowatt-hours, kilocalories and BTU, so you can compare an electricity bill, a food label and an air-conditioner spec side by side.
| Amount | Joules | kWh | kcal | BTU |
|---|---|---|---|---|
| 100 Wh | 360,000 | 0.100 | 86 | 341 |
| 1 MJ | 1,000,000 | 0.278 | 239 | 948 |
| 1 kWh | 3,600,000 | 1.000 | 860 | 3,412 |
| 1,000 kcal | 4,184,000 | 1.162 | 1,000 | 3,966 |
| 10,000 BTU | 10,550,559 | 2.931 | 2,522 | 10,000 |
Kilojoule labels and tiny electronvolts
Food labels in Australia and New Zealand lead with kilojoules, not Calories. Their reference adult diet of 8,700 kJ works out to 2,079 kcal. If you're tracking calories from an Australian product, divide the kJ figure by 4.184.
Electronvolts sit at the other extreme. One eV is 1.602 × 10⁻¹⁹ J, so converting everyday amounts gives huge or tiny numbers: one kilowatt-hour is about 2.25 × 10²⁵ eV. The tool switches to scientific notation for any result below 0.000001, so read the exponent before copying the figure.