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 joule?
The joule is the SI base unit of energy. It is the standard unit for work, heat, and electrical energy in physics, engineering, and scientific measurement worldwide.
Real-world uses
The joule is the SI unit of energy used in physics, chemistry, and nutrition (food energy in some countries is labelled in kilojoules). Electrical energy, mechanical work, and heat transfer are all measured in joules. One joule is the energy to lift a small apple about 1 metre.
History
Named after James Prescott Joule, the English physicist who demonstrated the mechanical equivalent of heat in the 1840s, establishing that heat and mechanical work are interchangeable forms of energy. The joule was adopted as the SI energy unit in 1960.
Common mistakes
Confusing joules with watts—a joule is a unit of energy, while a watt is a unit of power (1 W = 1 J/s). Also, assuming "calorie" and "joule" are equivalent without conversion: 1 cal = 4.184 J.
When is this conversion used?
Converting between British thermal unit and joule 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. Electricity bills use kilowatt-hours while physics calculations use joules. Converting between them is essential for energy audits, comparing appliance efficiency, and understanding power consumption.
Worked examples
1 British thermal unit = 1,055.05585262 joule
1 joule = 1 joule
How to convert British thermal unit to joule
To convert British thermal unit to joule, multiply the value by 1,055.05585262.
To convert joule back to British thermal unit, multiply by 0.00094782.
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 joule
| British thermal unit | joule |
|---|---|
| 0.1 | 105.50558526 |
| 0.5 | 527.52792631 |
| 1 | 1,055.05585262 |
| 2 | 2,110.11170524 |
| 5 | 5,275.2792631 |
| 10 | 10,550.5585262 |
| 25 | 26,376.3963155 |
| 50 | 52,752.792631 |
| 100 | 105,505.585262 |
| 250 | 263,763.963155 |
| 500 | 527,527.92631 |
| 1,000 | 1,055,055.85262 |
Common values
| British thermal unit | joule | |
|---|---|---|
| A food calorie (1 kcal) | 3.96566683 British thermal unit | 4,184 joule |
| A AA battery | 8.87156825 British thermal unit | 9,360 joule |
| Boiling a kettle | 398.08319053 British thermal unit | 420,000 joule |
| Daily human diet (2000 kcal) | 7,931.33366278 British thermal unit | 8,368,000 joule |
| 1 gallon of gasoline | 124,884.38377248 British thermal unit | 131,760,000 joule |
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.