Six millimeters is equal to 0.236 inches, according to calculations based on a conversion table published by the University of Arizona. Therefore, a kidney stone measuring 6 millimeters in length is less than a quarter of an inch long.
When considering the size of a 6-millimeter kidney stone, it may be useful to compare it to the diameter of a dime, the smallest U.S. coin. A dime is 17.91 millimeters in diameter, notes the U.S. Mint. This is significantly longer than 6 millimeters. If an individual were to cut a dime in half, each piece would be nearly 9 millimeters wide — still longer than a kidney stone measuring 6 millimeters in length.