How long does it take for blood to regenerate?

For each pint of blood lost, the human body takes 24 hours to regenerate plasma and four to six weeks to replace red blood cells, according to the American Red Cross.

The U.S. Department of Health and Human Services approves intravenous blood transfusions as a way to replenish blood quickly. Each year, 5 million Americans receive fresh blood after surgeries, injuries or serious illnesses.

Four main components make up blood, as stated by the University of Rochester Medical Center. Red blood cells carry oxygen, white blood cells boost immune functions, platelets aid clotting and plasma facilitates transport throughout the body.