Convert BTU to Kilojoules
BTU to kilojoules is the conversion you need when a heating or cooling rating is in British thermal units but you want a tidy metric energy figure. One BTU is exactly 1.05505585262 kilojoules, so the two numbers stay close in size — handy when you want an easy mental check.
British thermal units to Kilojoules conversion table
| British thermal units (BTU) | Kilojoules (kJ) |
|---|---|
| 1 | 1.055056 |
| 2 | 2.110112 |
| 3 | 3.165168 |
| 5 | 5.275279 |
| 10 | 10.550559 |
| 20 | 21.101117 |
| 50 | 52.752793 |
| 100 | 105.505585 |
| 500 | 527.527926 |
| 1,000 | 1,055.055853 |
The formula
To convert BTU to kilojoules, multiply the number of BTU by 1.05505585262:
kilojoules = BTU × 1.05505585262
A worked example
Say you have 500 BTU and want it in kilojoules:
500 × 1.05505585262 = 527.52793 kJ
So 500 BTU is about 527.5 kilojoules.
Why the number is exact
The International Table BTU is defined as exactly 1055.05585262 joules, and a kilojoule is exactly 1000 joules. Dividing one by the other gives exactly 1.05505585262 kilojoules per BTU — a fixed, defined figure rather than a measured or rounded one.
When you'll use it
Putting an appliance's BTU rating into the kilojoules used on nutrition and energy labels in many countries, comparing heating output across metric and imperial specs, or working a problem where the rest of the numbers are already in kilojoules.
Frequently asked questions
How many kilojoules are in a BTU?
Exactly 1.05505585262 kilojoules. Since a kilojoule is 1000 joules, this is just the joules-per-BTU figure shifted three decimal places.
Roughly how many kilojoules is a BTU?
A little over one — about 1.055 kJ. So a BTU and a kilojoule are close cousins, which makes kilojoules an easy metric unit to sanity-check BTU ratings against.
Is the BTU to kilojoules conversion exact?
Yes, for the International Table BTU. It is defined as exactly 1.05505585262 kilojoules, with nothing rounded away.