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 calorie (thermochemical)?
The thermochemical calorie is a unit of energy equal to approximately 4.184 joules. It is used in chemistry and physics to express small heat quantities, particularly in thermochemical experiments.
Real-world uses
The thermochemical calorie (4.184 J) is used in chemistry for expressing heats of reaction, specific heat capacities of substances, and calorimetry experiments. It appears in older scientific literature and some chemistry textbooks, particularly in calorimetric calculations.
History
The calorie was first defined by Nicolas Clément in 1824 as the heat needed to raise 1 gram of water by 1°C. The thermochemical calorie (exactly 4.184 J) was later standardized for precise scientific use, distinguishing it from other calorie definitions.
Common mistakes
Confusing the small calorie (cal, 4.184 J) with the large Calorie/kilocalorie (Cal/kcal, 4,184 J) used in food labelling. Also, several slightly different definitions of the calorie exist (thermochemical, 15°C, IT), which differ by fractions of a percent.
When is this conversion used?
Converting between British thermal unit and calorie (thermochemical) 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 = 252.16440072 calorie (thermochemical)
1 calorie (thermochemical) = 4.184 joule
How to convert British thermal unit to calorie (thermochemical)
To convert British thermal unit to calorie (thermochemical), multiply the value by 252.16440072.
To convert calorie (thermochemical) back to British thermal unit, multiply by 0.00396567.
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 calorie (thermochemical)
| British thermal unit | calorie (thermochemical) |
|---|---|
| 0.1 | 25.21644007 |
| 0.5 | 126.08220036 |
| 1 | 252.16440072 |
| 2 | 504.32880144 |
| 5 | 1,260.82200361 |
| 10 | 2,521.64400722 |
| 25 | 6,304.11001804 |
| 50 | 12,608.22003609 |
| 100 | 25,216.44007218 |
| 250 | 63,041.10018045 |
| 500 | 126,082.2003609 |
| 1,000 | 252,164.4007218 |
Common values
| British thermal unit | calorie (thermochemical) | |
|---|---|---|
| A food calorie (1 kcal) | 3.96566683 British thermal unit | 1,000 calorie (thermochemical) |
| A AA battery | 8.87156825 British thermal unit | 2,237.09369025 calorie (thermochemical) |
| Boiling a kettle | 398.08319053 British thermal unit | 100,382.40917782 calorie (thermochemical) |
| Daily human diet (2000 kcal) | 7,931.33366278 British thermal unit | 2,000,000 calorie (thermochemical) |
| 1 gallon of gasoline | 124,884.38377248 British thermal unit | 31,491,395.79349904 calorie (thermochemical) |
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.