Convert energy between joules, calories, kilocalories (food Calories), watt-hours, kilowatt-hours, BTU, and foot-pounds.
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| Unit | Equals |
|---|---|
| 1 Kilojoule | 1,000 Joules |
| 1 Calorie | 4.184 Joules |
| 1 Kilocalorie (Food Calorie) | 4,184 Joules |
| 1 Watt-hour | 3,600 Joules |
| 1 Kilowatt-hour | 3,600,000 Joules |
| 1 BTU | 1,055.05585262 Joules |
| 1 Foot-pound | 1.3558179483 Joules |
An energy converter changes a measurement of energy from one unit to another while representing the same physical quantity — 1 kilocalorie and 4,184 joules describe the same amount of energy, just counted in different units. Energy units show up across nutrition labels, electricity bills, physics coursework, and appliance ratings, and each field tends to default to a different unit.
This is one of the most common mix-ups in everyday energy measurement. The scientific "calorie" (lowercase c) is a small unit of energy — the amount needed to raise one gram of water by one degree Celsius. It's rarely useful on its own for describing food energy, because food contains far more energy than a handful of small calories would suggest.
So nutrition labels use the "Calorie" (capital C) instead — which is actually a kilocalorie, equal to 1,000 small calories. When a label says a snack has "200 Calories," it means 200 kilocalories, or 200,000 small calories.
In this converter, "Calories (cal)" refers to the small scientific calorie, and "Kilocalories / Food Calories (kcal)" refers to the unit used on nutrition labels. Always check which one a source means before comparing numbers.
The SI unit of energy, defined as the work done by one newton of force over one meter. It's the base unit this converter uses internally.
1,000 joules. Used on nutrition labels in many countries alongside or instead of kilocalories.
The small scientific calorie: 4.184 joules exactly. Common in chemistry.
1,000 small calories, or 4,184 joules. This is the unit meant by "Calories" on nutrition labels.
The energy used by a one-watt load running for one hour: 3,600 joules exactly.
1,000 watt-hours, or 3,600,000 joules. The standard unit electricity bills use to measure and charge for energy consumption.
The energy needed to heat one pound of water by one degree Fahrenheit: about 1,055.06 joules. Common in HVAC and heating/cooling equipment ratings.
An imperial unit of work or energy, equal to about 1.3558 joules. Used in mechanics and engineering, especially for torque-related contexts.
Energy conversions come up when tracking nutrition and diet against labels that mix Calories and kilojoules, reading electricity bills that bill in kWh, working through physics and engineering homework that uses joules, comparing heating and cooling equipment rated in BTU, and making sense of food labels from other countries that report energy differently than labels at home.
No. The "Calorie" (capital C) on nutrition labels is actually a kilocalorie — 1,000 small calories. A small calorie (lowercase c) is the scientific unit used in chemistry and physics. So "200 Calories" on a food label means 200 kilocalories, or 200,000 small calories.
One kilocalorie (food Calorie) equals 4,184 joules exactly.
Multiply the number of kilowatt-hours by 3,600,000 to get joules. For example, 2 kWh × 3,600,000 = 7,200,000 joules.
A British Thermal Unit (BTU) measures the energy needed to heat one pound of water by one degree Fahrenheit. It is commonly used to rate the heating and cooling capacity of furnaces, air conditioners, and water heaters.
One joule equals approximately 0.239006 small calories (0.000239006 kilocalories).
There are exactly 1,000 watt-hours in a kilowatt-hour.
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