Joules to British Thermal Units
Type a value in either box to convert between joules and British thermal units. The factor is 0.000947817.
| Joules | British Thermal Units |
|---|---|
| 1 J | 0.000948 BTU |
| 2 J | 0.001896 BTU |
| 3 J | 0.002843 BTU |
| 5 J | 0.004739 BTU |
| 10 J | 0.009478 BTU |
| 25 J | 0.023695 BTU |
| 50 J | 0.047391 BTU |
| 100 J | 0.094782 BTU |
How to use
- Enter a value in the Joules field.
- The British Thermal Units figure appears immediately — no button to press.
- Typing in the British Thermal Units field converts back to Joules the same way.
- Use the reference table for the values that come up most often.
Joules to British Thermal Units formula
The factor from joules to British thermal units is 0.00094781712.
BTU = J × 0.00094781712
Why this factor: the joule and the British thermal unit are both defined against the joule, so dividing one definition by the other gives 0.00094781712 directly. Both definitions are set out in full below.
To go the other way, divide by 0.00094781712 — or use the British Thermal Units to Joules converter, which is the same calculation reversed.
Worked example
Start with 2000 J. Multiply by 0.00094781712 to get 1.895634 BTU.
2000 J × 0.00094781712 = 1.895634 BTU
The converter above does this for any value you type, in either direction.
What is a joule?
The joule is the SI unit of energy — the work done by one newton acting over one meter.
Definition: Defined as 1 N·m, equivalently one watt-second. Named after James Prescott Joule.
Where it is used: All scientific energy calculations, food energy on European labels, and mechanical work.
What is a British thermal unit?
A BTU is the energy needed to raise one pound of water by one degree Fahrenheit.
Definition: The international-table BTU is about 1,055.056 joules.
Where it is used: US heating and air-conditioning capacity ratings, natural gas pricing, and boiler output.
Worth knowing: Air-conditioner ratings quoted as 'BTU' are really BTU per hour — a rate of cooling, not a quantity of energy.
Joules vs British Thermal Units
The joule is an SI unit while the British thermal unit is a US customary unit. That is why the factor between them is not a round number: the two systems were defined independently and only later tied together by exact agreement.
Frequently asked questions
How many British thermal units are in a joule?
One joule equals 0.00094781712 British thermal units.
What is the formula to convert joules to British thermal units?
Multiply the number of joules by 0.00094781712. To reverse it, divide by 0.00094781712 instead.
How do I convert British thermal units back to joules?
Divide by 0.00094781712, which is the same as multiplying by 1055.05585.
How many British thermal units are in 10 joules?
10 J works out to 0.009478 BTU.
Is there anything to watch out for with British thermal units?
Air-conditioner ratings quoted as 'BTU' are really BTU per hour — a rate of cooling, not a quantity of energy.
How is the joule defined?
Defined as 1 N·m, equivalently one watt-second. Named after James Prescott Joule.