The Planck energy is the unit of energy in the system of Planck units. It has the value:

*E _{p} = 1.96 × 10^{9}J*

In SI units, measurements of energy are made in Joules (usually given the symbol **J**). The Joule is convenient for everyday usage, such as measuring the energy produced by eating different types of foods (eating 1 gram of a carbohydrate provides around 16,000 J of energy) or determining the energy requirements of a light globe (a 60 W globe uses 60 J every second). We can also write Joules in terms of the units of length, time and mass:

1 Joule = 1kg m^{2} s^{-2}

A consequence of SI units is that the fundamental constants take on values that are not always convenient for including in equations:

Speed of light | c = 299792458 m s^{-1} |

Gravitational constant | G = 6.673(10) x 10^{-11} m^{3}kg^{-1}s^{-2} |

Plank’s constant (reduced) | = h/2π = 1.054571596(82) x 10^{-34}kg m^{2} s^{-1} |

Boltzmann constant | k = 1.3806502(24) x 10^{-23} kg m^{2} s^{-2} K^{-1} |

The Planck energy is found using Einstein’s famous formula relating energy and mass: *E _{p} = m_{p}c ^{2}*, with the Planck mass defined as:

By redefining the base units for length, mass and time in terms of the Planck units, the fundamental constants have the values:

*c* = *G* = = *k* = 1.

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