What is kilocalorie (dietary)?
A kilocalorie, written as Calorie with a capital C in nutrition contexts, is a unit of energy equal to 1,000 thermochemical calories. It is the standard unit used to express the energy content of food on nutrition labels globally.
Real-world uses
Kilocalories are the standard unit for food energy labelling in the United States (labelled as "Calories" with a capital C), dietary planning, and exercise energy expenditure. A typical adult needs about 2,000 kcal/day. Fitness trackers report calories burned in kcal.
History
Wilbur Atwater pioneered the use of kilocalories for food energy measurement in the 1890s. The confusing convention of using a capital-C "Calorie" to mean kilocalorie originated in American nutritional science and persists on US food labels today.
Common mistakes
The most common mistake is confusing Calories (kcal) with calories (cal)—they differ by a factor of 1,000. When food labels say "100 Calories," they mean 100 kilocalories. Also, assuming all macronutrients have the same caloric density (fat has 9 kcal/g vs 4 kcal/g for protein and carbohydrates).
What is calorie (thermochemical)?
The thermochemical calorie is a unit of energy equal to approximately 4.184 joules. It is used in chemistry and physics to express small heat quantities, particularly in thermochemical experiments.
Real-world uses
The thermochemical calorie (4.184 J) is used in chemistry for expressing heats of reaction, specific heat capacities of substances, and calorimetry experiments. It appears in older scientific literature and some chemistry textbooks, particularly in calorimetric calculations.
History
The calorie was first defined by Nicolas Clément in 1824 as the heat needed to raise 1 gram of water by 1°C. The thermochemical calorie (exactly 4.184 J) was later standardized for precise scientific use, distinguishing it from other calorie definitions.
Common mistakes
Confusing the small calorie (cal, 4.184 J) with the large Calorie/kilocalorie (Cal/kcal, 4,184 J) used in food labelling. Also, several slightly different definitions of the calorie exist (thermochemical, 15°C, IT), which differ by fractions of a percent.
When is this conversion used?
Nutritional information is labelled in kilocalories in some countries and kilojoules in others, making this conversion important for dietary planning and food science.
Worked examples
1 kilocalorie (dietary) = 1,000 calorie (thermochemical)
1 calorie (thermochemical) = 4.184 joule
How to convert kilocalorie (dietary) to calorie (thermochemical)
To convert kilocalorie (dietary) to calorie (thermochemical), multiply the value by 1,000.
To convert calorie (thermochemical) back to kilocalorie (dietary), multiply by 0.001.
Measurement standards
The joule is the SI derived unit of energy, defined as one kilogram-metre-squared per second-squared (kg·m²/s²). The kilowatt-hour, equal to exactly 3.6 megajoules, is accepted for use with the SI by the BIPM for practical electricity metering.
Did you know?
A single bolt of lightning releases roughly 1 to 5 gigajoules of energy, yet only a small fraction reaches the ground as electrical current. Most of the energy dissipates as light, heat, and the thunder shockwave.
Quick reference: kilocalorie (dietary) to calorie (thermochemical)
| kilocalorie (dietary) | calorie (thermochemical) |
|---|---|
| 0.1 | 100 |
| 0.5 | 500 |
| 1 | 1,000 |
| 2 | 2,000 |
| 5 | 5,000 |
| 10 | 10,000 |
| 25 | 25,000 |
| 50 | 50,000 |
| 100 | 100,000 |
| 250 | 250,000 |
| 500 | 500,000 |
| 1,000 | 1,000,000 |
Common values
| kilocalorie (dietary) | calorie (thermochemical) | |
|---|---|---|
| A food calorie (1 kcal) | 1 kilocalorie (dietary) | 1,000 calorie (thermochemical) |
| A AA battery | 2.23709369 kilocalorie (dietary) | 2,237.09369025 calorie (thermochemical) |
| Boiling a kettle | 100.38240918 kilocalorie (dietary) | 100,382.40917782 calorie (thermochemical) |
| Daily human diet (2000 kcal) | 2,000 kilocalorie (dietary) | 2,000,000 calorie (thermochemical) |
| 1 gallon of gasoline | 31,491.3957935 kilocalorie (dietary) | 31,491,395.79349904 calorie (thermochemical) |
Available Energy units
More kilocalorie (dietary) conversions
- Convert kilocalorie (dietary) to joule
- Convert kilocalorie (dietary) to kilojoule
- Convert kilocalorie (dietary) to kilowatt hour
- Convert kilocalorie (dietary) to calorie (thermochemical)
- Convert kilocalorie (dietary) to watt hour
- Convert kilocalorie (dietary) to megajoule
- Convert kilocalorie (dietary) to electronvolt
- Convert kilocalorie (dietary) to British thermal unit
- Convert kilocalorie (dietary) to therm (US)
Assumption: calorie means thermochemical calorie, and therm means US therm.