Some interesting facts about
how much blood a person can safely donate. For example, males and females aged
between 18 and 60 has approximately 5 to 6 litres of blood. As long the person
donating weighs more than 45 kg, they can donate around 350 ml (one unit) of
blood every three months.
Before they draw the blood,
they usually do some blood testing to check for things such as iron levels, blood type and anything else that will
help them understand what type of blood they are receiving. The blood volume a
person loses in the donation process usually replenishes itself within 24
As others have said, 1 pint (473 ml). You do need to meet a minimum weight requirement, and be healthy. You cannot have an illness within the two weeks prior to donating.
Old question, but worth a response:
The average adult has about 10 pints of blood in his body. Roughly 1 pint is given during a donation. A healthy donor may donate red blood cells every 56 days or Power Red every 112 days. A healthy donor may donate platelets as few as 7 days apart, but a maximum of 24 times a year.