Exsanguination is losing enough blood to cause death. A person does not have to lose all of their blood to exsanguinate. People can die from losing half to two-thirds of their blood.

The average adult has about 4 to 6 liters of blood (9 to 12 US pints) in their body. The average man has more blood than the average woman, and people who weigh more or are taller than others have more blood. This means a person can die from losing 2 ¹/₂ to 4 liters of blood. To compare, this is five to eight times as much blood as people usually give in a blood donation.