This page converts BTUs per pound degree Fahrenheit into kilojoules per kilogram-kelvin using the factor 4.1868, and shows the reverse figure alongside it. Both units measure how much energy raises one kilogram by one degree, which is why one number does the whole job.
Thermodynamic tables use kJ/(kg·K) to keep the numbers near one. The US unit, numerically almost identical to cal/(g·°C) by design of the BTU.
Below the calculator there is a step table for the values people look up most, and a second table putting real how much energy raises one kilogram by one degree figures into kilojoules per kilogram-kelvin so the number you get has something to be compared against.
The formula
BTUs per pound degree Fahrenheit- The amount you are converting, in BTUs per pound degree Fahrenheit
4.1868- The exact number of kilojoules per kilogram-kelvin in one BTU per pound degree Fahrenheit
kilojoules per kilogram-kelvin- The converted result
How it works, step by step
- Enter the value in BTUs per pound degree Fahrenheit.
- It is multiplied by 4.1868, the exact factor between the two units.
- The answer is shown in kilojoules per kilogram-kelvin, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
Olive oil: 0.471 BTU/(lb·°F) in kilojoules per kilogram-kelvin
At 0.471 BTU/(lb·°F) (olive oil), the same quantity in kilojoules per kilogram-kelvin is 0.471 × 4.1868 = 1.97198 kJ/(kg·K). One BTU per pound degree Fahrenheit is 4.1868 kilojoules per kilogram-kelvin, so the numbers grow as expected.
Dry air: 0.24 BTU/(lb·°F) in kilojoules per kilogram-kelvin
Take dry air, roughly 0.24 BTU/(lb·°F). The conversion is a single multiplication — 0.24 × 4.1868 — giving 1.00483 kJ/(kg·K). Because the relationship is proportional, doubling the input doubles the answer to 2.00966 kJ/(kg·K).
How to read your score
Frequently asked questions
How many kilojoules per kilogram-kelvin are in one BTU per pound degree Fahrenheit?
Exactly 4.1868. Every figure on this page is that one number multiplied by your input, so the only rounding is at the display step.
What is the formula to convert BTUs per pound degree Fahrenheit to kilojoules per kilogram-kelvin?
kilojoules per kilogram-kelvin = BTUs per pound degree Fahrenheit × 4.1868. Reversed, BTUs per pound degree Fahrenheit = kilojoules per kilogram-kelvin ÷ 4.1868, which is the same as multiplying by 0.238845896627.
Which is the bigger unit, the BTU per pound degree Fahrenheit or the kilojoule per kilogram-kelvin?
The BTU per pound degree Fahrenheit. One BTU per pound degree Fahrenheit equals 4.1868 kilojoules per kilogram-kelvin.
What does this quantity actually measure?
Both units measure how much energy raises one kilogram by one degree. That is why a single factor is enough: there is no temperature offset and no material property involved, unlike conversions that cross between different quantities.
What is a BTU per pound degree Fahrenheit?
The US unit, numerically almost identical to cal/(g·°C) by design of the BTU.
What is a kilojoule per kilogram-kelvin?
Thermodynamic tables use kJ/(kg·K) to keep the numbers near one.
Why does my answer differ from another converter?
Almost always because the other tool rounded the factor before multiplying. This page keeps full double precision through the calculation and rounds only for display, and it prints the factor it used so you can see where any difference came from.
Is there a quick way to do BTU/(lb·°F) to kJ/(kg·K) in my head?
Plenty of people do this in their head: multiply by 4.2 instead of using the exact factor 4.1868. At 100 that shortcut gives 420 kilojoules per kilogram-kelvin, off by 1.32 kilojoules per kilogram-kelvin or about 0.32%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Btus Per Pound Degree Fahrenheit to kilojoules per kilogram-kelvin reference tables
| Btus Per Pound Degree Fahrenheit | Kilojoules Per Kilogram-Kelvin |
|---|---|
| 0.5 BTU/(lb·°F) | 2.0934 kJ/(kg·K) |
| 1 BTU/(lb·°F) | 4.1868 kJ/(kg·K) |
| 2 BTU/(lb·°F) | 8.3736 kJ/(kg·K) |
| 3 BTU/(lb·°F) | 12.5604 kJ/(kg·K) |
| 5 BTU/(lb·°F) | 20.934 kJ/(kg·K) |
| 10 BTU/(lb·°F) | 41.868 kJ/(kg·K) |
| 20 BTU/(lb·°F) | 83.736 kJ/(kg·K) |
| 25 BTU/(lb·°F) | 104.67 kJ/(kg·K) |
| 50 BTU/(lb·°F) | 209.34 kJ/(kg·K) |
| 75 BTU/(lb·°F) | 314.01 kJ/(kg·K) |
| 100 BTU/(lb·°F) | 418.68 kJ/(kg·K) |
| 250 BTU/(lb·°F) | 1046.7 kJ/(kg·K) |
| 500 BTU/(lb·°F) | 2093.4 kJ/(kg·K) |
| 1000 BTU/(lb·°F) | 4186.8 kJ/(kg·K) |
| 5000 BTU/(lb·°F) | 20,934 kJ/(kg·K) |
Exact factor: 1 BTU per pound degree Fahrenheit = 4.1868 kilojoules per kilogram-kelvin.
| Quantity | BTU/(lb·°F) | kJ/(kg·K) |
|---|---|---|
| Dry air | 0.24 BTU/(lb·°F) | 1.005 kJ/(kg·K) |
| Aluminium | 0.2142 BTU/(lb·°F) | 0.897 kJ/(kg·K) |
| Concrete | 0.2102 BTU/(lb·°F) | 0.88 kJ/(kg·K) |
| Steel | 0.117 BTU/(lb·°F) | 0.49 kJ/(kg·K) |
| Water | 0.9989 BTU/(lb·°F) | 4.182 kJ/(kg·K) |
| Olive oil | 0.4705 BTU/(lb·°F) | 1.97 kJ/(kg·K) |
Published reference values, converted with the same factor this page uses.