A: A unit of whole blood is 450 milliliters, which is about 0.9510 U.S. pint. For components of blood, one unit is the amount of that substance that would normally be found in one unit of whole...
Last time I gave blood, they take 470mls of blood, plus four test tubes partially filled as samples for testing. Some tests would be to check I don't have any disease, others for lab tests I suppose.
I'm afraid that this question may have confused you, as Red Blood Cells do not actually carry any Blood at all. This is because Blood is comprised of Red Blood Cells.
The answer to your question...