Convert energy units — joules, calories, kilowatt-hours, BTU, kilojoules.
| Unit | Name | Value |
|---|---|---|
| J | Joule | 4.184 |
| kJ | Kilojoule | 0.004184 |
| kcal | Kilocalorie (Cal) | 0.001 |
| kWh | Kilowatt-hour | 0.0000011622222 |
| BTU | BTU | 0.0039656512 |
Formula: BTU = Calorie × 0.003966
Multiply any calorie value by 0.003966 to get btu.
Reverse: Calorie = BTU × 252.2
Common calorie values — factor: 1 cal = 0.003966 BTU
| Calorie (cal) | BTU (BTU) | Context |
|---|---|---|
| 1 cal | 0.003966 BTU | 1 cal |
| 5 cal | 0.01983 BTU | 5 cal |
| 10 cal | 0.03966 BTU | Small candy |
| 50 cal | 0.1983 BTU | 50 cal |
| 100 cal | 0.3966 BTU | Short walk |
| 500 cal | 1.983 BTU | Snack |
| 1,000 cal | 3.966 BTU | Light meal |
| 5,000 cal | 19.83 BTU | Meal |
| 1e+04 cal | 39.66 BTU | Large meal |
| 5e+04 cal | 198.3 BTU | Daily intake fraction |
| 1e+05 cal | 396.6 BTU | 100 kcal |
| 5e+05 cal | 1,983 BTU | 500 kcal workout |
| 1e+06 cal | 3,966 BTU | 1 Mcal |
| 1.000e+09 cal | 3.966e+06 BTU | 1 Gcal |
| 1.000e+12 cal | 3.966e+09 BTU | 1 Tcal |
1 cal = 0.003966 BTU. Memorize for instant estimates.
Use 0.004 as a quick mental multiplier.
Multiply result by 252.2 to recover the original cal value.
Sizes heating and cooling systems rated in BTU/hour for US buildings.
Certifies boiler output and efficiency ratings in BTU/hour.
Prices natural gas supply and usage in BTU and therms.
Calculates heating loads and heat loss in BTU for US properties.
Rates commercial refrigeration and ice-making capacity in BTU.
Specifies heat exchanger capacity and furnace output in BTU/hour.
The calorie (cal) was defined in 1824 as the heat needed to raise 1 gram of water by 1°C. There are two versions: the small calorie (cal = 4.184 J) and the large calorie or kilocalorie (kcal = 4,184 J), which is the 'Calorie' used in nutrition.
The calorie remains standard in chemistry for heat of reaction measurements. In the US, food packaging uses 'Calories' (with capital C) which are actually kilocalories — a persistent source of confusion.
Interesting fact: The confusion between cal and kcal means that a food label saying '200 Calories' actually means 200 kcal = 200,000 cal = 836,800 joules. The SI unit for food energy is the kilojoule.
The British Thermal Unit (BTU) is the traditional Imperial energy unit, defined as the heat required to raise 1 pound of water by 1°F. It equals 1,055.06 joules and has been used since the 19th century in heating, air conditioning, and gas billing.
BTU remains dominant in US HVAC: air conditioners and heaters are rated in BTU/hour. Natural gas is priced in therms (100,000 BTU) in the US. Furnaces are rated in BTU/hour output.
Interesting fact: A typical US home furnace is rated at 80,000–120,000 BTU/hour. One BTU is roughly the energy released by burning one kitchen match. The US natural gas pipeline system delivers about 25 quadrillion BTU (quads) per year.
Converting calorie to btu is common across energy, nutrition, engineering, and science. Different sectors use different energy units — joules in physics, kcal in nutrition, kWh in electricity, and BTU in HVAC — making accurate conversion essential for cross-disciplinary work and international comparisons.
Quick reference: 5 cal = 0.01983 BTU and 10 cal = 0.03966 BTU. Reverse: 1 BTU = 252.2 cal. Exact factor: 1 cal = 0.003966 BTU.
All conversions use IEEE 754 double-precision arithmetic, accurate to at least 8 significant figures.