The average blood volume of an adult is 5 L, comprising about 3 L of plasma and 2 L of erythrocytes (varies with age, weight, and gender).

1. In nonobese individuals, the blood volume varies in direct proportion to the body weight, averaging 70 mL/kg for lean men and women.

2. The greater the ratio of fat to body weight, the less is the blood volume in milliliters per kilogram because adipose tissue has a decreased vascular supply.

The normal hematocrit is about 45% for men and postmenopausal women and about 38% for menstruating women, with a range of approximately ±5%.