Energy Converter
Convert joules, calories, kilowatt-hours and BTU.
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The Energy Converter translates a quantity of energy between seven units: joule, kilojoule, calorie, kilocalorie, watt-hour, kilowatt-hour and BTU. It links figures that usually live in separate worlds, such as the kWh "units" on an electricity bill, the kcal on a food label, the joules in a physics problem and the BTU used in heating and cooling specifications.
How a conversion is calculated
Enter the amount in Value, choose its unit in From, pick a target in To and press Convert. Every unit is stored as a number of joules, so the tool multiplies your value by the From factor and divides by the To factor. Alongside the main answer it lists the same amount in all the other units, rounded to six decimal places.
The factors behind each unit
| Unit | Joules |
|---|---|
| 1 kilojoule | 1,000 |
| 1 calorie | 4.184 |
| 1 kilocalorie | 4,184 |
| 1 watt-hour | 3,600 |
| 1 kilowatt-hour | 3,600,000 |
| 1 BTU | 1,055.06 |
The calorie here is the thermochemical calorie of exactly 4.184 J. The International Table calorie (4.1868 J) is slightly larger, a difference of about 0.07% that only matters in precise engineering work. The BTU factor is the International Table value of 1,055.05585 J rounded to two decimals. A watt-hour is simply one watt sustained for an hour: 1 W × 3,600 s = 3,600 J.
Worked example: a day's food in electricity units
An adult diet of 2,000 kcal sounds nothing like a power bill, but convert it: enter 2000, From kilocalorie, To kilowatt-hour.
2,000 × 4,184 J = 8,368,000 J; 8,368,000 ÷ 3,600,000 = 2.324444 kWh
The other rows give 8,368 kJ, 2,324.444444 Wh and 7,931.302485 BTU. So a full day's food energy equals about two and a third "units" of electricity. Note that nutrition labels mean kilocalories when they print "Calories" with a capital C.
Electricity bills and appliances
A "unit" on an Indian electricity bill is one kilowatt-hour. To estimate what an appliance uses, multiply its power in kilowatts by the hours it runs: a 1.5 kW geyser switched on for 2 hours uses 3 kWh. Entering 3 kWh here shows that this is 10,800 kJ, or about 10,236 BTU. For the rupee cost of those units at your tariff, use the electricity bill calculator.
Energy versus power
This tool converts amounts of energy, not rates of use. Watts, kilowatts, BTU per hour and "tons" of air-conditioning capacity are all power, meaning energy per unit of time. A 1.5-ton AC is rated at 18,000 BTU per hour of cooling (one ton of refrigeration is 12,000 BTU/h), and that rating cannot be entered here as if it were a quantity. Its cooling output is also different from the electricity it draws, which the label lists separately in watts.