Calorie to British Thermal Unit Converter
One Calorie equals 0.003965666831 British Thermal Unit (1 cal = 0.003965666831 BTU). Multiply a Calorie value by 0.003965666831 to get the equivalent in British Thermal Unit. Use the calculator above for instant results, or follow the formula, worked examples, and reference table below.
Formula
BTU = cal × 0.003965666831
Multiply the Calorie value by 0.003965666831 to get the equivalent value in British Thermal Unit.
Example Conversions
1 Calorie (cal)
0.003965666831 British Thermal Unit (BTU)
5 Calorie (cal)
0.01982833416 British Thermal Unit (BTU)
10 Calorie (cal)
0.03965666831 British Thermal Unit (BTU)
25 Calorie (cal)
0.09914167078 British Thermal Unit (BTU)
100 Calorie (cal)
0.3965666831 British Thermal Unit (BTU)
Conversion Table
| Calorie (cal) | British Thermal Unit (BTU) |
|---|---|
| 0.1 | 0.0003965666831 |
| 0.5 | 0.001982833416 |
| 1 | 0.003965666831 |
| 2 | 0.007931333663 |
| 5 | 0.01982833416 |
| 10 | 0.03965666831 |
| 25 | 0.09914167078 |
| 50 | 0.1982833416 |
| 100 | 0.3965666831 |
| 250 | 0.9914167078 |
| 500 | 1.982833416 |
| 1000 | 3.965666831 |
How to Convert Manually
Use these steps to convert Calorie values to British Thermal Unit without the calculator.
- Write down the value in Calorie (cal) that you want to convert.
- Multiply that value by 0.003965666831.
- For example, 10 Calorie × 0.003965666831 = 0.03965666831 British Thermal Unit.
- Label the result as British Thermal Unit (BTU).
Relative Size Comparison
This chart shows the visual difference in size between exactly one Calorie and one British Thermal Unit.
About Calorie and British Thermal Unit
The calorie (small calorie) is exactly 4.184 joules — the thermochemical convention, originally the heat to warm one gram of water by 1 °C. Chemistry uses it; food 'Calories' are actually kilocalories. The British thermal unit is about 1,055.06 joules — the heat to raise one pound of water by 1 °F. US heating and cooling equipment is rated in BTU per hour. One Calorie equals 0.003965666831 British Thermal Unit (1 cal = 0.003965666831 BTU). Calorie to British Thermal Unit conversion comes up most often in chemistry heat calculations and in scientific literature, typically when figures need restating for air conditioner and furnace ratings in the US.
Precision and Rounding: Energy factors mix exact definitions (1 kWh = 3,600,000 J; 1 cal = 4.184 J thermochemical) with measured conventions (1 BTU ≈ 1,055.056 J). Nutrition and utility bills round to whole units; engineering heat calculations should keep the full factor until the final step.
Conversion factors per NIST Special Publication 811 and the BIPM SI Brochure (9th edition) (reference).
Worked Example
15 Calorie equals 0.05948500247 British Thermal Unit.
15 cal × 0.003965666831 = 0.05948500247 BTU
FAQ
How do I convert Calorie to British Thermal Unit?
Multiply the Calorie value by 0.003965666831 to get the equivalent value in British Thermal Unit.
What is the formula for Calorie to British Thermal Unit?
The formula is BTU = cal × 0.003965666831.
How many British Thermal Unit are in 1 Calorie?
1 Calorie equals 0.003965666831 British Thermal Unit.
Can I convert British Thermal Unit back to Calorie?
Yes. 1 British Thermal Unit equals 252.1644007 Calorie, and the related converter can reverse the calculation.
What are common names for Calorie and British Thermal Unit?
Calorie is shown as cal and may also be searched as calorie, calories, small calorie. British Thermal Unit is shown as BTU and may also be searched as btu, british thermal unit.
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