Convert energy units — joules, calories, kilowatt-hours, BTU, kilojoules.
| Unit | Name | Value |
|---|---|---|
| kJ | Kilojoule | 0.001 |
| cal | Calorie | 0.23900574 |
| kcal | Kilocalorie (Cal) | 0.00023900574 |
| kWh | Kilowatt-hour | 2.7777778e-7 |
| BTU | BTU | 0.00094781339 |
Formula: Calorie = Joule × 0.239
Multiply any joule value by 0.239 to get calorie.
Reverse: Joule = Calorie × 4.184
Common joule values — factor: 1 J = 0.239 cal
| Joule (J) | Calorie (cal) | Context |
|---|---|---|
| 0.001 J | 0.000239 cal | 1 mJ |
| 0.1 J | 0.0239 cal | Heartbeat |
| 1 J | 0.239 cal | Lift apple 10cm |
| 4.184 J | 1 cal | 1 calorie |
| 100 J | 23.9 cal | Sprinting 1 sec |
| 1,000 J | 239 cal | 1 kJ |
| 4,184 J | 1,000 cal | 1 kcal food |
| 1e+04 J | 2,390 cal | 10 kJ |
| 1e+05 J | 2.39e+04 cal | 100 kJ |
| 1.055e+06 J | 2.522e+05 cal | 1 BTU |
| 3.6e+06 J | 8.604e+05 cal | 1 kWh |
| 1e+08 J | 2.39e+07 cal | ~100 MJ |
| 1.000e+09 J | 2.39e+08 cal | 1 GJ |
| 1.000e+12 J | 2.390e+11 cal | 1 TJ |
| 1.000e+15 J | 2.390e+14 cal | 1 PJ |
J ÷ 4.184 = cal. Exact.
One thermochemical calorie = 4.184 J.
cal × 4.184 = J.
Uses joules as the SI unit for all energy, work, and heat calculations.
Calculates kinetic energy, potential energy, and work in joules.
Measures reaction enthalpies, bond energies, and heat of solution in joules.
Converts between power (watts) and energy (joules = watt-seconds).
Measures fracture energy and impact resistance in joules.
Applies the first law of thermodynamics with energy in joules.
The joule is the SI derived unit of energy, work, and heat, defined as the energy transferred when a force of one newton moves an object one meter. It was named after James Prescott Joule, the English physicist who established the mechanical equivalent of heat in the 1840s.
The joule is universal in physics and engineering: kinetic energy (½mv²), potential energy (mgh), electrical energy (VIt), and heat are all measured in joules. One joule is the energy needed to lift a 100g apple one meter against gravity.
Interesting fact: The human heart expends about 1 joule of energy with each beat. A 60-watt light bulb uses 60 joules every second. The entire energy released by a 1-megaton nuclear weapon equals about 4.18 × 10¹⁵ joules.
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 joule 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 J = 1.195 cal and 10 J = 2.39 cal. Reverse: 1 cal = 4.184 J. Exact factor: 1 J = 0.239 cal.
All conversions use IEEE 754 double-precision arithmetic, accurate to at least 8 significant figures.