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 watt hour?
A watt hour is a unit of energy equal to the power of one watt sustained for one hour. It is used to measure small amounts of electrical energy consumption, particularly in battery capacities and portable electronics.
Real-world uses
Watt-hours measure the energy stored in or consumed from batteries, small electronics, and portable power stations. A smartphone battery holds roughly 10–15 Wh; a laptop battery 40–100 Wh. Solar panel output for small installations is often quoted in Wh per day.
History
The watt-hour emerged as a practical energy unit in the late 19th century with the commercialisation of electric power distribution. It offered a convenient scale between the joule (too small) and kilowatt-hour (too large) for everyday portable energy applications.
Common mistakes
Confusing watt-hours (energy) with watts (power). A device rated at 5 W running for 3 hours consumes 15 Wh. Also, treating Wh and mAh as interchangeable without knowing voltage: Wh = mAh × V ÷ 1000.
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) = 1.16222222 watt hour
1 watt hour = 3,600 joule
How to convert kilocalorie (dietary) to watt hour
To convert kilocalorie (dietary) to watt hour, multiply the value by 1.16222222.
To convert watt hour back to kilocalorie (dietary), multiply by 0.86042065.
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 watt hour
| kilocalorie (dietary) | watt hour |
|---|---|
| 0.1 | 0.11622222 |
| 0.5 | 0.58111111 |
| 1 | 1.16222222 |
| 2 | 2.32444444 |
| 5 | 5.81111111 |
| 10 | 11.62222222 |
| 25 | 29.05555556 |
| 50 | 58.11111111 |
| 100 | 116.22222222 |
| 250 | 290.55555556 |
| 500 | 581.11111111 |
| 1,000 | 1,162.22222222 |
Common values
| kilocalorie (dietary) | watt hour | |
|---|---|---|
| A food calorie (1 kcal) | 1 kilocalorie (dietary) | 1.16222222 watt hour |
| A AA battery | 2.23709369 kilocalorie (dietary) | 2.6 watt hour |
| Boiling a kettle | 100.38240918 kilocalorie (dietary) | 116.66666667 watt hour |
| Daily human diet (2000 kcal) | 2,000 kilocalorie (dietary) | 2,324.44444444 watt hour |
| 1 gallon of gasoline | 31,491.3957935 kilocalorie (dietary) | 36,600 watt hour |
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.