Calories to British Thermal Units
Type a value in either box to convert between calories and British thermal units. The factor is 0.00396567.
| Calories | British Thermal Units |
|---|---|
| 1 cal | 0.003966 BTU |
| 2 cal | 0.007931 BTU |
| 3 cal | 0.011897 BTU |
| 5 cal | 0.019828 BTU |
| 10 cal | 0.039657 BTU |
| 25 cal | 0.099142 BTU |
| 50 cal | 0.198283 BTU |
| 100 cal | 0.396567 BTU |
How to use
- Enter a value in the Calories field.
- The British Thermal Units figure appears immediately — no button to press.
- Typing in the British Thermal Units field converts back to Calories the same way.
- Use the reference table for the values that come up most often.
Calories to British Thermal Units formula
The factor from calories to British thermal units is 0.00396566683.
BTU = cal × 0.00396566683
Why this factor: the calorie and the British thermal unit are both defined against the joule, so dividing one definition by the other gives 0.00396566683 directly. Both definitions are set out in full below.
To go the other way, divide by 0.00396566683 — or use the British Thermal Units to Calories converter, which is the same calculation reversed.
Worked example
Take 2000 cal and multiply by the factor 0.00396566683: the result is 7.931334 BTU.
2000 cal × 0.00396566683 = 7.931334 BTU
The converter above does this for any value you type, in either direction.
What is a calorie?
A calorie is the energy needed to warm one gram of water by one degree Celsius.
Definition: The thermochemical calorie is defined as exactly 4.184 joules.
Where it is used: Chemistry and physics literature, and older engineering references.
Worth knowing: The 'calories' on a nutrition label are actually kilocalories — 1,000 of these. A 500-Calorie meal is 500 kcal, or about 2.1 million joules.
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.
Calories vs British Thermal Units
The calorie is a specialized 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 calorie?
One calorie equals 0.00396566683 British thermal units.
What is the formula to convert calories to British thermal units?
Multiply the number of calories by 0.00396566683. To reverse it, divide by 0.00396566683 instead.
How do I convert British thermal units back to calories?
Divide by 0.00396566683, which is the same as multiplying by 252.164401.
How many British thermal units are in 10 calories?
10 cal works out to 0.039657 BTU.
Is there anything to watch out for with calories?
The 'calories' on a nutrition label are actually kilocalories — 1,000 of these. A 500-Calorie meal is 500 kcal, or about 2.1 million joules.
How is the calorie defined?
The thermochemical calorie is defined as exactly 4.184 joules.