The SI unit of energy (and work) is the Joule (J), named after the famous British physicist James Prescott Joule .

• Joule (J): Defined as $1 \text{ J} = 1 \text{ N m}$ (Newton-metre). It is the standard unit in the International System of Units (SI) .
• Erg: This is the unit of energy in the CGS (centimetre-gram-second) system ($1 \text{ J} = 10^7 \text{ erg}$) .
• Calorie (cal): A common unit for heat energy ($1 \text{ cal} \approx 4.186 \text{ J}$) .
• Electron volt (eV): A unit commonly used in atomic and nuclear physics ($1 \text{ eV} \approx 1.6 \times 10^{-19} \text{ J}$) .