Energy Converter
Energy converter for joules, kilowatt-hours and BTU, with the small calorie and the food Calorie kept as separate rows rather than one ambiguous one.
Most used energy tools
Joules to Calories
The small calorie and the food Calorie kept apart, a factor of 1,000 error if merged.
Power Converter
The rate of energy use rather than the amount.
Watts to Horsepower
Power in three horsepower definitions.
Convert every unit at once
Enter a number.
Every energy converter on this site
Reference table
| Unit | In joules | Exact? |
|---|---|---|
| 1 kilojoule | 1,000 J | Exact |
| 1 calorie (thermochemical) | 4.184 J | Exact |
| 1 Calorie (food, kcal) | 4,184 J | Exact |
| 1 watt-hour | 3,600 J | Exact |
| 1 kilowatt-hour | 3,600,000 J | Exact |
| 1 BTU (International Table) | 1,055.05585 J | Rounded |
The two calories
The Calorie on a nutrition label is a kilocalorie, 1,000 of the calories used in physics. Both appear in this tool as separate rows because merging them is a factor of 1,000 error, the largest routine unit mistake there is.
The joules to calories page covers which is which and why the capital C convention isn't reliable.
kWh on your electricity bill
A kilowatt-hour is the energy used by a 1 kW appliance running for one hour, which is 3,600,000 joules. It is an energy unit despite containing a power unit in its name, and that is the source of most confusion about electricity bills.
Power is the rate; energy is the total. The power converter handles the rate side.
Common questions
How many joules in a calorie?
The small thermochemical calorie is exactly 4.184 joules. The food Calorie is exactly 4,184 joules.
How many joules in a kWh?
A kilowatt-hour is exactly 3,600,000 joules, or 3.6 megajoules. It is 1,000 watts sustained for 3,600 seconds, and since a watt is one joule per second the result is exact rather than rounded.
Is a kWh a unit of power or energy?
Energy. Power is the rate of energy use, measured in watts. A kilowatt-hour is what you get when you use a kilowatt for an hour.
What is a BTU?
The British thermal unit, roughly the energy to raise one pound of water by one degree Fahrenheit. It is about 1,055 joules and appears mainly on heating and cooling equipment.
Sources
- NIST Guide to the SI, Appendix B: Conversion Factors. National Institute of Standards and Technology. Source for every conversion factor on this page, and for which factors are exact rather than rounded.