Human Body

Blood and Circulation

How big are capillaries?

The diameter of a capillary is about 0.0003 inches (0.0076 millimeters), which is just about the same as a single red blood cell. A capillary is only about 0.04 inches (1 millimeter) long. If all the capillaries in a human body were placed end to end, the collective length would be approximately 25,000 miles (46,325 kilometers), which is slightly more than the circumference of the earth at the equator: 24,900 miles (46,139 kilometers).


This is a web preview of the "The Handy Science Answer Book" app. Many features only work on your mobile device. If you like what you see, we hope you will consider buying. Get the App