Hematologic Malignancies Center
Lifespan Cancer Institute

Facts about Blood

The average adult who weighs 150 to 180 pounds has about 1.2 to 1.5 gallons of blood in their body, accounting for about 7 percent of their weight. Four basic components — each with its own role — make up blood: red blood cells, white blood cells, platelets, and plasma. 

Red blood cells account for nearly all of the 45 percent of blood volume that is made up of cells. They are produced in the bone marrow at the astonishing rate of four billion to five billion each hour and circulate in the body for about 120 days. Hemoglobin, the protein inside red blood cells, carries oxygen to your tissues and removes carbon dioxide, a waste product, to be exhaled from your lungs. Misshapen red blood cells are indicators of pernicious anemia and sickle cell anemia.

White blood cells, called leukocytes, only account for one percent of your blood volume, but play a critical role in keeping you healthy. They protect against illness and disease by attacking invaders like viruses and bacteria. White blood cells also begin as stem cells produced in your bone marrow. 

There are three types of white blood cells — lymphocytes, monocytes, and granulocytes — and three main kinds of granulocytes, called neutrophils, eosinophils, and basophils.

Platelets, the smallest type of blood cells, control bleeding by helping clots form, enabling the injured tissue to heal. They develop from stem cells created in the bone marrow.

Plasma is the liquid portion of your blood that carries water and nutrients to your body’s tissues. It makes up a little more than half of your blood volume and is 90 percent water.

Learn more about blood disorders and cancers »