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: Kilojoule = Joule × 0.001
Multiply any joule value by 0.001 to get kilojoule.
Reverse: Joule = Kilojoule × 1000
Common joule values — factor: 1 J = 0.001 kJ
| Joule (J) | Kilojoule (kJ) | Context |
|---|---|---|
| 0.001 J | 1.000e-06 kJ | 1 mJ |
| 0.1 J | 0.0001 kJ | Heartbeat |
| 1 J | 0.001 kJ | Lift apple 10cm |
| 4.184 J | 0.004184 kJ | 1 calorie |
| 100 J | 0.1 kJ | Sprinting 1 sec |
| 1,000 J | 1 kJ | 1 kJ |
| 4,184 J | 4.184 kJ | 1 kcal food |
| 1e+04 J | 10 kJ | 10 kJ |
| 1e+05 J | 100 kJ | 100 kJ |
| 1.055e+06 J | 1,055 kJ | 1 BTU |
| 3.6e+06 J | 3,600 kJ | 1 kWh |
| 1e+08 J | 1e+05 kJ | ~100 MJ |
| 1.000e+09 J | 1e+06 kJ | 1 GJ |
| 1.000e+12 J | 1.000e+09 kJ | 1 TJ |
| 1.000e+15 J | 1.000e+12 kJ | 1 PJ |
J ÷ 1,000 = kJ. Exact — shift decimal 3 places.
Simple kilo prefix.
kJ × 1,000 = 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 kilojoule (kJ) equals 1,000 joules and is the practical energy unit for food, chemistry, and heating applications in metric countries. Food energy labels in Australia, Europe, and most of the world use kilojoules.
A dietary calorie (kcal) equals 4.184 kJ. A can of soda contains about 600 kJ. The specific heat of water (4.184 kJ/kg·°C) means heating 1 liter of water by 1°C requires 4.184 kJ.
Interesting fact: An average adult needs about 8,000-10,000 kJ (2,000-2,400 kcal) per day. Running a marathon burns approximately 12,500 kJ.
Converting joule to kilojoule 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 = 0.005 kJ and 10 J = 0.01 kJ. Reverse: 1 kJ = 1000 J. Exact factor: 1 J = 0.001 kJ.
All conversions use IEEE 754 double-precision arithmetic, accurate to at least 8 significant figures.