One micrometer, which is one millionth of a meter or approximately 1/25,000 of an inch. The tiny elements that make up a transistor on a chip are measured in micrometers and nanometers. See process technology.
Magnified 800 Times
This is an 800x magnification of a few bits of RAM from an early Motorola microcontroller. Although the actual size of what you see in this picture would fit on a pinhead, the elements in the devices on this chip are several microns wide, which is quite large by today's standards.