The size of the Planck length can be visualized as follows: if a particle or dot about 0.1 mm in size (which is at or near the smallest the unaided human eye can see) were magnified in size to be as large as the observable universe, then inside that universe-sized "dot", the Planck length would be roughly the size of an actual 0.1 mm dot. In other words, a 0.1 mm dot is halfway between the Planck length and the size of the observable universe on a logarithmic scale.
https://en.wikipedia.org/wiki/Planck_length