This box is 100 px in height and width. It is 1.2 inches across on my screen when displayed at 100% in my browser.

This box is 10 px in height and width: It is 0.12 inches across on my screen when displayed at 100% in my browser.

This box is 5 px in height and width: It is 0.06 inches across on my screen when displayed at 100% in my browser.

This box is 2 px in height and width: It is 0.024 inches across on my screen when displayed at 100% in my browser.

This box is 1 px in height and width: It is 0.012 inches across on my screen when displayed at 100% in my browser.

With my reading glasses I can see a box 1 px, approx 1/100 inch, across but probably not much smaller.