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 British thermal unit?
A British thermal unit (BTU) is an energy unit defined as the heat needed to raise one pound of water by one degree Fahrenheit. It is used in HVAC systems, heating and cooling equipment ratings, and natural gas billing in the United States.
Real-world uses
The British Thermal Unit is used in the United States for heating and cooling system ratings (furnaces, air conditioners), natural gas billing, and refrigeration. A typical home air conditioner might be rated at 12,000–24,000 BTU/h. Natural gas is often sold per therm (100,000 BTU).
History
The British Thermal Unit was proposed in the 1840s as the heat needed to raise one pound of water by one degree Fahrenheit. Despite its name, its primary use today is in the United States; the UK and most Commonwealth countries have transitioned to SI units for engineering applications.
Common mistakes
Confusing BTU (energy) with BTU/h (power). An air conditioner rated at "12,000 BTU" typically means 12,000 BTU per hour of heat removal capacity, not a fixed energy amount. Also mixing up the slightly different BTU definitions (IT, thermochemical, 39°F, 60°F).
When is this conversion used?
Converting between watt hour and British thermal unit is common when working across metric and imperial systems, such as international trade, travel between countries with different measurement standards, or following instructions from a different region.
Worked examples
1 watt hour = 3.41214163 British thermal unit
1 British thermal unit = 1,055.05585262 joule
How to convert watt hour to British thermal unit
To convert watt hour to British thermal unit, multiply the value by 3.41214163.
To convert British thermal unit back to watt hour, multiply by 0.29307107.
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 British thermal unit
| watt hour | British thermal unit |
|---|---|
| 0.1 | 0.34121416 |
| 0.5 | 1.70607082 |
| 1 | 3.41214163 |
| 2 | 6.82428327 |
| 5 | 17.06070817 |
| 10 | 34.12141633 |
| 25 | 85.30354083 |
| 50 | 170.60708166 |
| 100 | 341.21416331 |
| 250 | 853.03540828 |
| 500 | 1,706.07081656 |
| 1,000 | 3,412.14163313 |
Common values
| watt hour | British thermal unit | |
|---|---|---|
| A food calorie (1 kcal) | 1.16222222 watt hour | 3.96566683 British thermal unit |
| A AA battery | 2.6 watt hour | 8.87156825 British thermal unit |
| Boiling a kettle | 116.66666667 watt hour | 398.08319053 British thermal unit |
| Daily human diet (2000 kcal) | 2,324.44444444 watt hour | 7,931.33366278 British thermal unit |
| 1 gallon of gasoline | 36,600 watt hour | 124,884.38377248 British thermal unit |
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.