Weight is a good guideline for blood volume in people of average build. This is why we set a minimum weight limit of 7st 12lbs (50 kg) because if more than 13% of blood volume is taken there is more risk of the donor feeling faint after donating.
Not surprisingly, the one factlet most often offered up as revealed truth is wholly false: Your hair and nails do not continue to grow after you die; it's all optical illusion. The sorry fact of the matter is that we dehydrate after dying. Our flesh dries and, in so doing, pulls away from nails and hair.
Cells of hair follicles that make hair, and nail matrix that make nails, die along with the rest of the body and are incapable of further growth. The misconception probably arises from the fact that skin shrinks and retracts a bit after death, making hair and nails appear somewhat longer than before death.