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.
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).
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 watt hour = 0.86042065 kilocalorie (dietary)
1 kilocalorie (dietary) = 4,184 joule
How to convert watt hour to kilocalorie (dietary)
To convert watt hour to kilocalorie (dietary), multiply the value by 0.86042065.
To convert kilocalorie (dietary) back to watt hour, multiply by 1.16222222.
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: watt hour to kilocalorie (dietary)
| watt hour | kilocalorie (dietary) |
|---|---|
| 0.1 | 0.08604207 |
| 0.5 | 0.43021033 |
| 1 | 0.86042065 |
| 2 | 1.7208413 |
| 5 | 4.30210325 |
| 10 | 8.6042065 |
| 25 | 21.51051625 |
| 50 | 43.0210325 |
| 100 | 86.04206501 |
| 250 | 215.10516252 |
| 500 | 430.21032505 |
| 1,000 | 860.4206501 |
Common values
| watt hour | kilocalorie (dietary) | |
|---|---|---|
| A food calorie (1 kcal) | 1.16222222 watt hour | 1 kilocalorie (dietary) |
| A AA battery | 2.6 watt hour | 2.23709369 kilocalorie (dietary) |
| Boiling a kettle | 116.66666667 watt hour | 100.38240918 kilocalorie (dietary) |
| Daily human diet (2000 kcal) | 2,324.44444444 watt hour | 2,000 kilocalorie (dietary) |
| 1 gallon of gasoline | 36,600 watt hour | 31,491.3957935 kilocalorie (dietary) |
Available Energy units
More watt hour conversions
- Convert watt hour to joule
- Convert watt hour to kilojoule
- Convert watt hour to kilowatt hour
- Convert watt hour to calorie (thermochemical)
- Convert watt hour to kilocalorie (dietary)
- Convert watt hour to megajoule
- Convert watt hour to electronvolt
- Convert watt hour to British thermal unit
- Convert watt hour to therm (US)
Assumption: calorie means thermochemical calorie, and therm means US therm.