Calculator
What the BTU Converter does
BTU Converter: 1 BTU = 1.055055853 kJ, so multiply a british thermal unit value by 1.055055853 to get kilojoule, or divide to go back. Example: 1 BTU = 1.055055853 kJ.
Point it at Value, From and To and it returns Result, How it was calculated and Reverse conversion. The result recalculates on every keystroke without a button press or a page reload.
It is mostly used by people following a recipe or spec written elsewhere. Two industries often use the same word for slightly different quantities.
Everything happens inside this page. Nothing you type is sent to a server, and there is nothing for us to store.
The sections that follow cover the fields, the method, and one full example computed from the defaults.
What do the BTU Converter fields mean?
The BTU Converter uses 3 inputs. The form opens pre-filled, so the fastest way in is usually to overwrite the one field you actually care about.
| Field | What to enter | Default |
|---|---|---|
| Value | required | 1 |
| From | choose from Joule (J), Kilojoule (kJ), Megajoule (MJ), Calorie (thermochemical) (cal), Kilocalorie (food calorie) (kcal) or Watt hour (Wh) | British thermal unit (BTU) |
| To | choose from Joule (J), Kilojoule (kJ), Megajoule (MJ), Calorie (thermochemical) (cal), Kilocalorie (food calorie) (kcal) or Watt hour (Wh) | Kilojoule (kJ) |
How does the BTU Converter work?
Both units are converted through energy's base unit (J), so any of the 12 units in the dropdowns can be paired in either direction without loss of accuracy.
Definitions are taken from the SI system where one exists, and from CODATA or the IAU where a unit is established by measurement. No factor is rounded before the calculation.
Worked example
These are the values the BTU Converter loads by default, and the result it produces from them. These are the tool’s own default values and the result they produce, not an invented illustration.
| Value | 1 |
|---|---|
| From | British thermal unit (BTU) |
| To | Kilojoule (kJ) |
| Result | 1.055055853 kJ |
|---|---|
| How it was calculated | 1 BTU = 1.055055853 kJ, so 1 × 1.055055853 = 1.055055853 kJ |
| Reverse conversion | 0.94781712 BTU (if you meant 1 kJ) |
The British thermal unit (BTU)
1 BTU (International Table definition) equals exactly 1,055.05585262 joules, historically defined as the energy needed to raise 1 pound of water by 1°F, and still the standard unit for heating and cooling appliance ratings in the US.
Worth knowing
- Air conditioner and furnace capacity in the US is rated in BTUs per hour (often just called "BTU" informally): a typical window air-conditioning unit might be rated around 5,000 to 12,000 BTU/h, while a whole-house central unit could be well over 24,000 BTU/h.
- US natural gas and heating-oil billing is often expressed in therms (1 therm = 100,000 BTU) or MBtu, while most of the rest of the world bills household energy in kilowatt-hours or by cubic metres of gas directly: a genuine obstacle when comparing US and international energy costs.
- Despite the name, the "British" thermal unit today is used almost exclusively in the United States: the UK itself moved to metric energy units (joules, kWh) decades ago for virtually all practical purposes.
Definitions: BIPM SI Brochure · NIST reference on units
How to use it
- Enter Value.
- Pick a value for From: the options are Joule (J), Kilojoule (kJ), Megajoule (MJ), Calorie (thermochemical) (cal), Kilocalorie (food calorie) (kcal) or Watt hour (Wh).
- Pick a value for To: the options are Joule (J), Kilojoule (kJ), Megajoule (MJ), Calorie (thermochemical) (cal), Kilocalorie (food calorie) (kcal) or Watt hour (Wh).
- The result appears as you type. There is no button to press.
- You get Result, How it was calculated and Reverse conversion back.
- Both Copy Link and Print capture the current state, so pick whichever suits how you file things.
What this tool does not do
- Repeated conversions compound rounding, so convert once from the original value where you can.
- Conversion factors use SI definitions; some industries use their own rounded factors.
- It does not account for anything you did not enter, by definition.
- Results are only as good as the inputs. Check your units before reading anything into the output.
Frequently asked questions
Value, From and To, nothing else. A starting value is in place for each, which makes it easy to isolate the effect of a single variable.
With the values loaded when the page opens, result comes out as 1.055055853 kJ. It recalculates the moment an input changes, which makes comparing scenarios quick.
No. There is no account, no session and no storage. The values exist only while the tab is open.
It costs nothing, and there is no limit on repeat use.
The logic is straightforward and testable; the worked example above uses the tool’s own defaults so you can verify it yourself.