Here’s a list of all common energy units used in various measurement systems:

1. SI (Metric) Units:

• Joule (J) – The SI unit of energy, used widely in scientific contexts. It is defined as the energy transferred when a force of one newton acts over a distance of one meter.

• Watt-hour (Wh) – A derived unit of energy, equivalent to the energy consumed by a one-watt device running for one hour.

• Kilojoule (kJ) – A common multiple of the joule, where 1 kJ = 1000 J.

• Megajoule (MJ) – A larger unit, where 1 MJ = 1,000,000 J.
  
  

2. Imperial Units:

• British Thermal Unit (BTU) – A unit of energy used in the US and UK, defined as the amount of energy needed to heat one pound of water by one degree Fahrenheit.

• Foot-pound (ft-lb) – A unit of energy or work in the imperial system, used to measure torque or mechanical work.

• Calorie (cal) – Originally defined as the amount of energy needed to raise the temperature of 1 gram of water by 1°C.

• Kilocalorie (kcal) – Often referred to as a "food calorie," it is equal to 1000 calories.
  
  

3. Other Energy Units:

• Electronvolt (eV) – A unit of energy commonly used in physics, especially in atomic and particle physics. 1 eV is the energy gained by an electron when it is accelerated through a potential difference of one volt.

• Therm – A unit of heat energy used primarily in natural gas. 1 therm = 100,000 BTUs.

• Tonne of TNT (tonne of trinitrotoluene) – A unit of energy used to express large amounts of energy, especially in the context of explosions. 1 tonne of TNT = 4.184 × 10^9 joules.

• KiloWatt-hour (kWh) – Commonly used in electrical energy measurements, particularly for household electricity usage. It is equivalent to using 1,000 watts for one hour.
  
  

4. Specialized Energy Units:

• Quantum of Action (ħ or h-bar) – A unit of energy used in quantum mechanics.

• Solar Luminosity (L⊙) – A unit used in astrophysics to represent the total energy emitted by the Sun.

• Planck Energy (Eₚ) – A unit of energy in the Planck scale, defined in terms of fundamental constants in physics.
  
  

Energy Conversion Formulas Between Units:

Here are some key conversion relationships between various energy units:

1. Joules to other units:
   
   

   • 1 Joule = 1 watt-second (Ws)

   • 1 Joule = 0.239 calories (cal)

   • 1 Joule = 0.000947817 BTU

   • 1 Joule = 9.478 x 10⁻⁶ kilocalories (kcal)

   • 1 Joule = 6.242 x 10¹³ electronvolts (eV)
     
     

2. Kilojoules to other units:
   
   

   • 1 kJ = 1000 Joules

   • 1 kJ = 0.239005736 calories

   • 1 kJ = 0.000947817 BTU
     
     

3. Calories to Joules:
   
   

   • 1 cal = 4.184 Joules
     
     

4. Kilocalories to Joules:
   
   

   • 1 kcal = 4184 Joules
     
     

5. BTUs to Joules:
   
   

   • 1 BTU = 1055.056 Joules
     
     

6. Kilowatt-hours (kWh) to Joules:
   
   

   • 1 kWh = 3.6 × 10⁶ Joules
     
     

7. Therms to Joules:
   
   

   • 1 therm = 1.055 × 10⁶ Joules
     
     

8. Electronvolts to Joules:
   
   

   • 1 eV = 1.602 × 10⁻¹⁹ Joules