Convert energy units — joules, calories, kilowatt-hours, BTU, kilojoules.
| Unit | Name | Value |
|---|---|---|
| J | Joule | 1055.06 |
| kJ | Kilojoule | 1.05506 |
| cal | Calorie | 252.16539 |
| kcal | Kilocalorie (Cal) | 0.25216539 |
| kWh | Kilowatt-hour | 0.00029307222 |
Formula: Calorie = BTU × 252.2
Multiply any btu value by 252.2 to get calorie.
Reverse: BTU = Calorie × 0.003966
Common btu values — factor: 1 BTU = 252.2 cal
| BTU (BTU) | Calorie (cal) | Context |
|---|---|---|
| 1 BTU | 252.2 cal | Match |
| 10 BTU | 2,522 cal | 10 BTU |
| 100 BTU | 2.522e+04 cal | Space heater second |
| 1,000 BTU | 2.522e+05 cal | 1 kBTU |
| 3,412 BTU | 8.604e+05 cal | 1 kWh |
| 1e+04 BTU | 2.522e+06 cal | 10 kBTU |
| 1e+05 BTU | 2.522e+07 cal | 1 therm |
| 1e+06 BTU | 2.522e+08 cal | 1 MMBTU |
| 1e+07 BTU | 2.522e+09 cal | 10 MMBTU |
| 1e+08 BTU | 2.522e+10 cal | 100 MMBTU |
| 1.000e+09 BTU | 2.522e+11 cal | 1 billion BTU |
| 1.000e+10 BTU | 2.522e+12 cal | 10 billion BTU |
| 1.000e+12 BTU | 2.522e+14 cal | 1 quad fraction |
| 1.000e+15 BTU | 2.522e+17 cal | 1 quad |
| 1.000e+18 BTU | 2.522e+20 cal | 1000 quads |
1 BTU = 252.2 cal. Memorize for instant estimates.
Use 252.2 as a quick mental multiplier.
Multiply result by 0.003966 to recover the original BTU 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 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.
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.
Converting btu to calorie 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 BTU = 1261 cal and 10 BTU = 2522 cal. Reverse: 1 cal = 0.003966 BTU. Exact factor: 1 BTU = 252.2 cal.
All conversions use IEEE 754 double-precision arithmetic, accurate to at least 8 significant figures.