Blood makes up about 7% of your body's weight.
The average adult has 10 pints of blood in his or her body. One unit of blood is roughly the equivalent of one pint.
This proportion is much greater in children, and slightly different in men and women.
Men, on average, have eight to ten pints while women have five to eight pints. That is just over a gallon or 4 - 5 litres for men and slightly less for women.
Larger people and populations can go much higher, up to 8-12 pints depending on the size of the person.