According to the National Library of Medicine, the site of blood cell formation is the bone marrow. Kimball's Biology Pages states there are two types of blood cells: red blood cells, or erythrocytes, and white blood cells, or leukocytes.
According to the School of Life Sciences at Arizona State University, bone marrow is the soft tissue found inside of bones. Merck Manuals explains how all blood cells arise from one type of cell: the hematopoietic stem cell. Because blood cells have short lives, they must be replenished constantly. White blood cells live from a few hours to a few days; red blood cells survive for about 120 days.
Red blood cells make up 45 percent of the volume of blood whereas white blood cells comprise only 1 percent of the blood volume, per the National Library of Medicine. The bone marrow makes about two million red blood cells every second.