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.
Death puts a stop to the supply of glucose, and therefore to fingernail growth. A similar process occurs for hair. Each hair sits within a follicle that drives its growth. At the base of the follicle is the hair matrix, a group of cells that divide to produce the new cells that make hair strands longer.