The tip of your hair is about 0.1 millimeters (mm), or 100 micrometers (µm), wide. If you assume that the tip is roughly circular, and the area of a circle is pi times radius squared (3.14 X 50µm^2), then the area of the tip is about 7,850 µm. We're assuming a 2 µm long *E. coli* cell is 1.25 µm wide, so its area is length times width, or 2 µm x 1.25 µm, which equals 2.5 µm squared. Divide 7,850 µm by 2.5 µm and you find out that roughly 3,140 *E. coli* could fit on the tip of your hair.