An average adult man weighing 160 pounds contains one and a quarter gallons of blood, or 10 pints. Estimation of blood volume is based on gender, age, weight, amount of lean body mass and even altitude: people who live at higher altitudes possess more blood to provide extra oxygen.
People who weigh less generally carry less blood. Body fat percentage is a major factor in blood volume, as fat contains less blood than muscle; thus, if two people have the same weight, the person who has more fat would actually have a lower blood volume even if he appears to be larger. Gender affects body fat composition in ways that are not entirely known, although sex hormones play a role. Because women are generally shorter and have higher body fat percentages than men, they generally have lower blood volumes. An average woman who is 5 feet tall and weighs 100 pounds has a little less than a gallon of blood in her veins.