system
Given the following post, respond as if you're commenting on Reddit:
human
How did Max Planck calculate a Planck Length?
gpt
Essentially you have three constants which relate to different areas of Physics.  There is planck's constant hbar which relates to quantum mechanics,  the speed of light c,  which is to do with relativity,  and the universal gravitational constant G,  which relates to gravity. 

There is only one way to combine these three to get a length which is

L = sqrt ( hbar  G / c^3 ) =1.61 ×10^-35

By dimensional analysis, this should occur as a natural length scale when dealing with the quantisation of gravitation and the curvature of space. It also occurs in an entropy calculation for black holes

S = A / (4 L)^2

With A the area of the event horizon.