100,000 km of vessels: a historical estimate

The figure of about 100,000 km is often repeated as the total length of human blood vessels. However, it is linked to early capillary calculations by August Krogh that used assumptions about capillary density and a very large muscle mass. A modern review of muscle microcirculation calls 100,000 km a memorable but enduring overestimate. Total network length is model-dependent rather than a simple direct measurement.