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 electronvolt?
An electronvolt is a unit of energy equal to the work done on an electron by a potential difference of one volt, approximately 1.602 × 10⁻¹⁹ joules. It is used in atomic physics, particle physics, and quantum mechanics.
Real-world uses
The electronvolt is the standard energy unit in particle physics, atomic physics, and semiconductor science. X-ray photon energies are measured in keV; visible light photons in eV (about 1.8–3.1 eV); nuclear reactions in MeV; and particle accelerator energies in GeV or TeV.
History
The electronvolt came into use in the early 20th century with the development of quantum mechanics and experimental atomic physics. As physicists began measuring energies of electrons and photons, the eV provided a convenient unit far smaller than the joule but appropriate for subatomic-scale phenomena.
Common mistakes
Confusing the electronvolt with a unit of voltage—it is a unit of energy equal to the kinetic energy gained by one electron accelerated through a potential difference of one volt (1 eV = 1.602 × 10⁻¹⁹ J). Also mixing up the scale prefixes (keV, MeV, GeV, TeV) when discussing different physical phenomena.
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) = 2.611447e+22 electronvolt
1 electronvolt = 1.602177e-19 joule
How to convert kilocalorie (dietary) to electronvolt
To convert kilocalorie (dietary) to electronvolt, multiply the value by 2.611447e+22.
To convert electronvolt back to kilocalorie (dietary), multiply by 3.829294e-23.
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 electronvolt
| kilocalorie (dietary) | electronvolt |
|---|---|
| 0.1 | 2.611447e+21 |
| 0.5 | 1.305724e+22 |
| 1 | 2.611447e+22 |
| 2 | 5.222895e+22 |
| 5 | 1.305724e+23 |
| 10 | 2.611447e+23 |
| 25 | 6.528618e+23 |
| 50 | 1.305724e+24 |
| 100 | 2.611447e+24 |
| 250 | 6.528618e+24 |
| 500 | 1.305724e+25 |
| 1,000 | 2.611447e+25 |
Common values
| kilocalorie (dietary) | electronvolt | |
|---|---|---|
| A food calorie (1 kcal) | 1 kilocalorie (dietary) | 2.611447e+22 electronvolt |
| A AA battery | 2.23709369 kilocalorie (dietary) | 5.842052e+22 electronvolt |
| Boiling a kettle | 100.38240918 kilocalorie (dietary) | 2.621434e+24 electronvolt |
| Daily human diet (2000 kcal) | 2,000 kilocalorie (dietary) | 5.222895e+25 electronvolt |
| 1 gallon of gasoline | 31,491.3957935 kilocalorie (dietary) | 8.223812e+26 electronvolt |
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.