Calories to BTU
Convert calories (cal) to btu (BTU). Both measure work and power, and the conversion comes up in nutrition, electricity, fitness work.
The Formula
``
btu = calories × 0.00396566683139
calories = btu × 252.164400722
`
One calory is 0.003966 btu, and one BTU is 252.1644 calories.
Conversion Table
| Calories | BTU |
|---|---|
| 1 cal | 0.003966 BTU |
| 2 cal | 0.007931 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 |
| 500 cal | 1.9828 BTU |
| 1,000 cal | 3.9657 BTU |
The Other Direction
| BTU | Calories |
|---|---|
| 1 BTU | 252.1644 cal |
| 2 BTU | 504.3288 cal |
| 5 BTU | 1,260.82 cal |
| 10 BTU | 2,521.64 cal |
| 25 BTU | 6,304.11 cal |
| 50 BTU | 12,608.22 cal |
| 100 BTU | 25,216.44 cal |
| 500 BTU | 126,082.2 cal |
| 1,000 BTU | 252,164.4 cal |
What Each Unit Is
Calories (cal) — the energy to raise one gram of water by one degree Celsius, or 4.184 joules — the "small" calorie. A 19th-century thermal unit, displaced by the joule in physics but retained in nutrition.
BTU (BTU) — the energy to raise one pound of water by one degree Fahrenheit, or 1,055 joules. The imperial thermal unit, still standard for US heating, cooling and gas.
A Sense of Scale
A gram of sugar holds about 4,000 small calories- A window air conditioner is 5,000–12,000 BTU/h
- US furnaces are rated in BTU
Precision
The factor 0.00396566683139 is rounded. For engineering work carry more digits than the table above, and round only at the end — rounding at each step compounds.
Watch Out For
- Food labels say "calorie" but mean kilocalorie — 1,000 of these. A 200-calorie snack is 200 kcal, or 837 kJ.
In Code
`javascript
const calorieToBtu = (value) => value * 0.00396566683139;
``
Where This Conversion Comes Up
- Nutrition
- Electricity
- Fitness
- Heating
- Fuel
How Many Decimals Do You Need?
Rounding the factor costs accuracy, and how much depends on the factor. Converting 137 cal with the factor truncated at each decimal place:
| Decimals kept | Factor | 137 cal becomes | Error |
|---|---|---|---|
| 0 | 0 | 0 | 100.0000% |
| 1 | 0 | 0 | 100.0000% |
| 2 | 0 | 0 | 100.0000% |
| 3 | 0.004 | 0.548 | 0.8658% |
| 4 | 0.004 | 0.548 | 0.8658% |
The right number of significant figures is set by your input, not by the converter. If you measured calories to three significant figures, the answer in btu is only good to three — writing more digits claims precision the measurement never had.