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 therm (US)?
A US therm is a unit of energy equal to 100,000 BTU. It is used by gas utility companies in the United States as the standard billing unit for natural gas consumption.
Real-world uses
The therm is used in the United States and United Kingdom for natural gas billing. One therm equals 100,000 BTU (approximately 29.3 kWh). Residential gas bills in the US often list consumption in therms. It is also used in industrial gas metering and procurement contracts.
History
The therm was introduced as a practical unit for natural gas billing in the early 20th century, when gas supply companies needed a convenient large-scale energy unit for residential and commercial customers. It consolidated prior inconsistent measurement practices in the gas industry.
Common mistakes
Confusing the therm with the BTU—1 therm = 100,000 BTU. Also, the US therm and the UK therm differ slightly (the UK therm is based on 105.5 MJ, while the US therm is exactly 100,000 BTU ≈ 105.48 MJ). Not to be confused with the thermie (a metric unit of heat).
When is this conversion used?
Converting British thermal unit to therm (US) is useful in the energy domain when comparing values across different measurement standards or applying formulas that require a specific unit.
Worked examples
1 British thermal unit = 0.00001 therm (US)
1 therm (US) = 105,506,000 joule
How to convert British thermal unit to therm (US)
To convert British thermal unit to therm (US), multiply the value by 0.00001.
To convert therm (US) back to British thermal unit, multiply by 100,000.39309578.
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 therm (US)
| British thermal unit | therm (US) |
|---|---|
| 0.1 | 9.999961e-07 |
| 0.5 | 0.000005 |
| 1 | 0.00001 |
| 2 | 0.00002 |
| 5 | 0.00005 |
| 10 | 0.0001 |
| 25 | 0.00025 |
| 50 | 0.0005 |
| 100 | 0.001 |
| 250 | 0.00249999 |
| 500 | 0.00499998 |
| 1,000 | 0.00999996 |
Common values
| British thermal unit | therm (US) | |
|---|---|---|
| A food calorie (1 kcal) | 3.96566683 British thermal unit | 0.00003966 therm (US) |
| A AA battery | 8.87156825 British thermal unit | 0.00008872 therm (US) |
| Boiling a kettle | 398.08319053 British thermal unit | 0.00398082 therm (US) |
| Daily human diet (2000 kcal) | 7,931.33366278 British thermal unit | 0.07931302 therm (US) |
| 1 gallon of gasoline | 124,884.38377248 British thermal unit | 1.24883893 therm (US) |
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.