A unit of time in an absolute system of units devised by Max Planck, about 5.391 247 × 10⁻⁴⁴ second¹. Symbol, *t*_{P}. Algebraically, it is

where * c* = the speed of light, *
G* = Newtonian gravitational constant, and
*ħ* = the reduced Planck's constant.

From the equations, you can see that a velocity of 1 Planck length per Planck time is the speed of light.

1. This is the 2018 CODATA value. For the most up-to-date value, see NIST's CODATA pages: https://www.physics.nist.gov/cgi-bin/cuu/Value?plkt

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Last revised: 28 September 2011.