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).
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?
Converting between British thermal unit and watt hour 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 British thermal unit = 0.29307107 watt hour
1 watt hour = 3,600 joule
How to convert British thermal unit to watt hour
To convert British thermal unit to watt hour, multiply the value by 0.29307107.
To convert watt hour back to British thermal unit, multiply by 3.41214163.
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: British thermal unit to watt hour
| British thermal unit | watt hour |
|---|---|
| 0.1 | 0.02930711 |
| 0.5 | 0.14653554 |
| 1 | 0.29307107 |
| 2 | 0.58614214 |
| 5 | 1.46535535 |
| 10 | 2.9307107 |
| 25 | 7.32677675 |
| 50 | 14.65355351 |
| 100 | 29.30710702 |
| 250 | 73.26776754 |
| 500 | 146.53553509 |
| 1,000 | 293.07107017 |
Common values
| British thermal unit | watt hour | |
|---|---|---|
| A food calorie (1 kcal) | 3.96566683 British thermal unit | 1.16222222 watt hour |
| A AA battery | 8.87156825 British thermal unit | 2.6 watt hour |
| Boiling a kettle | 398.08319053 British thermal unit | 116.66666667 watt hour |
| Daily human diet (2000 kcal) | 7,931.33366278 British thermal unit | 2,324.44444444 watt hour |
| 1 gallon of gasoline | 124,884.38377248 British thermal unit | 36,600 watt hour |
Available Energy units
More British thermal unit conversions
- Convert British thermal unit to joule
- Convert British thermal unit to kilojoule
- Convert British thermal unit to kilowatt hour
- Convert British thermal unit to calorie (thermochemical)
- Convert British thermal unit to kilocalorie (dietary)
- Convert British thermal unit to watt hour
- Convert British thermal unit to megajoule
- Convert British thermal unit to electronvolt
- Convert British thermal unit to therm (US)
Assumption: calorie means thermochemical calorie, and therm means US therm.