Standard units defined in the International System of Units.
Units representing power consumed over time, used in grids and batteries.
Units based on water heating capacity, common in thermodynamics and HVAC.
Subatomic, mechanical, and classical CGS unit structures.
Energy Conversion Guide
Joule & SI Energy
The Joule (J) is the base SI unit of energy, defined as the work done by a force of 1 Newton moving an object through a distance of 1 meter (1 J = 1 N·m = 1 W·s). Kilojoules (kJ) and Megajoules (MJ) are commonly used in mechanical systems and dietary calculations.
Electrical Power & Capacity
Watt-hours (W·h) and Kilowatt-hours (kW·h) define electrical energy. 1 kW·h is the amount of work consumed by a 1-kilowatt electrical appliance running for 1 hour, equivalent to 3.6 Megajoules (MJ) or 1 unit of household electricity.
Caloric & Imperial Thermal Units
A calorie (cal) represents the heat needed to raise the temperature of 1 gram of water by 1°C. The kilocalorie (1 kcal = 1000 cal) is the standard food energy unit. The British thermal unit (BTU) is used in heating, ventilation, and air conditioning (HVAC) systems.
Mechanical Work & Subatomic Scale
On the atomic scale, physicists use the Electronvolt (eV), defined as the kinetic energy gained by a single electron accelerating through an electric potential difference of one volt. The Erg is the standard CGS unit (1 erg = 10⁻⁷ J). Foot-pound force (ft·lbf) is standard in mechanical engineering work.
Key Conversion Relations
| Unit | = Joules (J) |
|---|---|
| 1 J | 1 J (base) |
| 1 mJ | 0.001 J |
| 1 kJ | 1,000 J |
| 1 MJ | 1,000,000 J |
| 1 Wh | 3,600 J |
| 1 kWh | 3,600,000 J |
| 1 MWh | 3,600,000,000 J |
| 1 hph | ≈ 2,684,520 J |
| 1 cal | 4.1868 J |
| 1 kcal | 4,186.8 J |
| 1 BTU | ≈ 1,055.06 J |
| 1 thm | ≈ 1.05506 × 10⁸ J |
| 1 erg | 0.0000001 J |
| 1 eV | 1.602176634 × 10⁻¹⁹ J |
| 1 ft·lbf | ≈ 1.35582 J |
Frequently Asked Questions
What is the difference between power and energy?
Power is the rate at which energy is used (measured in Watts), whereas energy is the total capacity to perform work over time (measured in Joules or Watt-hours). Energy = Power × Time.
Why are there different types of calories?
The standard unit is the International Steam Table Calorie (cal = 4.1868 J), which is used here. In nutrition, a "Calorie" with a capital C actually refers to a kilocalorie (kcal or 1000 standard calories).
How is household electricity billed?
Power utility companies charge based on Kilowatt-hours (kW·h). 1 kW·h is equivalent to running a 100-watt light bulb continuously for 10 hours.