The diameter of an average human hair is about 70 micrometers, or 0.07 millimeters. On the other hand, a red blood cell has a diameter of approximately 7 to 8 micrometers. To determine how many red blood cells could fit across the diameter of a human hair, we can do a simple calculation.
Taking the average diameter of a red blood cell as 7.5 micrometers, we can divide the diameter of the hair by the diameter of a red blood cell:
70 micrometers (diameter of hair) / 7.5 micrometers (diameter of red blood cell) ≈ 9.33.
This means that approximately 9 to 10 red blood cells could fit across the width of a single strand of human hair. This fascinating comparison highlights just how tiny red blood cells are and gives us a sense of their scale in relation to other small structures in the human body.