Attojoule is 1e-18 joule units.
Attojoules to BTU Converter — aJ to BTU
Convert Attojoule (aJ) to BTU (BTU) using the exact conversion factor (1 attojoule = 9.478171e-22 btu). See the formula, worked examples, conversion table, history, and common uses.
Attojoules to BTU converter
Converter
Energy Converter
Convert joules, calories, kilowatt-hours, BTU, electronvolts, therms, and mechanical work units.
Context values
Some unit families need one extra value for a physically accurate result.
British thermal unit.
Result = input x 1e-18 / 1055.055853.
Energy uses the joule as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Attojoules to BTU
Attojoule and BTU both measure energy, and the conversion is especially useful for comparing nutrition labels (kilocalories) against scientific energy figures (joules). Specifically: Attojoule is 1e-18 joule units, and british thermal unit.
Formula
btu = attojoules × 9.478171e-22
This factor comes from each unit's defined relationship to the category's base unit: 1 attojoule equals 1e-18 base units, and 1 btu equals 1055.05585262 base units, so dividing one by the other gives the direct attojoule-to-btu factor of 9.478171e-22.
Simple example
1 aJ × 9.478171e-22 = 9.478171e-22 BTU
1 attojoule = 9.478171e-22 btu.
Real-world example
100 aJ × 9.478171e-22 = 9.478171e-20 BTU
100 attojoules = 9.478171e-20 btu.
Conversion table
| Attojoule (aJ) | BTU (BTU) |
|---|---|
| 1 aJ | 9.478171e-22 BTU |
| 10 aJ | 9.478171e-21 BTU |
| 100 aJ | 9.478171e-20 BTU |
| 500 aJ | 4.739086e-19 BTU |
| 1,000 aJ | 9.478171e-19 BTU |
| 2,000 aJ | 1.895634e-18 BTU |
Reverse conversion: BTU to Attojoule
9.478171e-22 BTU × 1.055056e+21 = 0.9999999786 aJ
9.478171e-22 btu = 0.9999999786 attojoules.
attojoules = btu × 1.055056e+21
For a page dedicated to this direction, see BTU to Attojoule.
Understanding the Attojoule (aJ)
Attojoule is 1e-18 joule units.
Understanding the BTU
BTU (BTU) measures energy. A British thermal unit is defined as exactly 1,055.05585262 joules (the International Table BTU). It is classified as a US customary unit.
Where it's used: United States (HVAC, heating, and appliance energy ratings)
Uses of the BTU today
- Air conditioner and furnace capacity ratings in the US
- Water heater and appliance energy specifications
- US energy industry (natural gas is often billed via BTU content)
History of the BTU
The BTU originated in 19th-century steam engineering as the heat needed to raise one pound of water by one degree Fahrenheit, paralleling the calorie's metric definition. Several slightly different BTU values existed historically before the 'International Table' BTU was standardized at exactly 1,055.05585262 joules.
Historical origin. BTU was not the invention of a single named person; it developed through the process described above.
BTU — sources
- NIST Special Publication 811 — Documents the International Table BTU's exact joule equivalence.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many btu are in 1 attojoule?
1 attojoule equals 9.478171e-22 btu, using the exact defined conversion factor rather than an estimate.
How do I convert attojoule to btu?
Multiply the attojoule value by 9.478171e-22. The converter above does this instantly to whatever precision you set.
How do I convert btu back to attojoule?
Use the reverse factor: 1 btu equals 1.055056e+21 attojoules. You can also use the swap control in the converter above to flip the direction instantly.
What is a attojoule?
Attojoule (aJ) is a unit of energy.
What is a btu?
BTU (BTU) measures energy. A British thermal unit is defined as exactly 1,055.05585262 joules (the International Table BTU). It is classified as a US customary unit.
Is the attojoule to btu conversion exact?
Yes. A British thermal unit is defined as exactly 1,055.05585262 joules (the International Table BTU). That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.