According to Brookhaven National Laboratory, one unit of blood is roughly equivalent to one pint. With just one pint of blood, up to three lives can be saved.
Brookhaven National Laboratory explains that within one unit of blood there are several components, including red blood cells, white blood cells, plasma, platelets and cryoprecipitate. Each component of blood can be stored for differing amounts of time, with plasma lasting the longest. While red blood cells carry oxygen to the body's organs and tissue, white blood cells are the body's primary defense against infection. Platelets help blood to clot. Each ill person requires differing amounts of the components that make up blood depending on his condition.