Convert Calorie to British Thermal Unit (cal → BTU)
The calorie is the chemistry energy unit, equal to 4.184 joules and used in thermochemistry calculations.
Calorie to British Thermal Unit Conversion Table
10 common values| Calorie | British Thermal Unit |
|---|---|
| 1 cal | 0.003966 BTU |
| 10 cal | 0.039657 BTU |
| 100 cal | 0.396567 BTU |
| 500 cal | 1.982833 BTU |
| 1,000 cal | 3.965667 BTU |
| 5,000 cal | 19.828334 BTU |
| 10,000 cal | 39.656668 BTU |
| 50,000 cal | 198.28334 BTU |
| 100,000 cal | 396.56668 BTU |
| 500,000 cal | 1,982.8334 BTU |
How to Convert Calorie to British Thermal Unit Manually
Step by StepConverting calories to BTU is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.
- 1Take your value in caloriesStart with the number of calories (cal) you want to convert.
- 2Multiply by 0.003966The conversion factor from cal to BTU is 0.003966. Multiply your value by this number.
- 3Read the result in BTUThe result is your value in BTU (BTU).
Formula
Multiply the value in calories by 0.003966. For the reverse direction, multiply by 252.1644.
BTU = cal × 0.003966cal = BTU × 252.1644Tips
Use these in everyday conversions- 1 cal = 4.184 J. 1 kcal = 4184 J.
- Scientific "calorie" and nutrition "Calorie" differ by 1000×.
- Prefer joules in modern scientific writing.
Common Mistakes
Avoid these- Assuming "calories" on food labels means gram calories — they are kcal.
- Mixing gram calories and kilocalories in calculations.
- Confusing calorie (energy) with calorimeter (apparatus).
About Calorie and British Thermal Unit
What is the Calorie?
The calorie equals exactly 4.184 joules (the 'thermochemical calorie') and is the historical unit for heat in chemistry and physics. It was originally defined as the heat needed to raise 1 gram of water by 1°C (a definition that varied slightly with starting temperature, hence multiple 'calories' — 4.184 J was set as the exact thermochemical convention). The calorie is widely used in older physics and chemistry literature for reaction energies, specific heat capacities, and thermodynamic calculations. Note: this 'small calorie' (lowercase c) is 1/1000 of the food Calorie (capital C) used in nutrition. The chemistry calorie relates to the joule (4.184 J = 1 cal), the kilocalorie (1,000 cal = 1 kcal = 1 food Calorie), and the BTU (1 BTU ≈ 252 cal). Modern SI usage in scientific publications has largely replaced the calorie with the joule, but it persists in medical and chemistry contexts.
- Thermodynamics and older physics texts
- Chemistry energy calculations
- Some engineering heat-transfer contexts
Raising 1 g of water 1 °C: 1 cal. A 100 kcal snack = 100,000 small calories.
What is the British Thermal Unit?
The British thermal unit (BTU) equals approximately 1,055.06 joules and is the standard unit in American HVAC, gas appliances, and air-conditioner ratings. Originally defined as the heat needed to raise 1 pound of water by 1°F, the BTU is the imperial counterpart to the calorie. American gas utilities measure delivered heat in BTUs or therms (1 therm = 100,000 BTU), and air conditioners are rated by their cooling capacity in BTU per hour (a typical window AC is 5,000–12,000 BTU/h, central AC for a medium home is 24,000–60,000 BTU/h). Furnaces are similarly rated. The BTU relates to the joule (1 BTU ≈ 1,055 J), the calorie (1 BTU ≈ 252 cal), the watt-hour (1 BTU ≈ 0.293 Wh), and the therm (100,000 BTU = 1 therm). Outside the United States, the BTU is rare; metric countries use kilojoules or kilowatt-hours for the same applications.
- US air-conditioner sizing
- US heating-system capacity
- Natural gas billing in some US regions
Window AC: 5000–12,000 BTU/h. Central AC: 24,000–60,000 BTU/h. Home furnace: 60,000–100,000 BTU/h.