A grain of sand has a diameter of slightly over 1 mm and the average diameter of a human cell is 8 micrometers. Putting them into common terms (meters) gives: 1.03 * 10^-3 m and 8*10^-6 m, respectively. Dividing the two to give a ratio leads to a value of (1.03*10^-3)/(8*10^-6), or 128.75 times longer for the grain of sand.
