How to estimate the DNA density in human sperm head?
Find, or calculate, a value for the volume of the sperm head.

Find a value for the size of the human genome (haploid or diploid?)

Convert the genome size, which will probably in Giga basepairs, into mass (I suggest picograms).

Divide mass by volume to get a density, pg &mu;m-3

Refinement - does the sperm nucleus take up all of the head volume? Do you need to factor this in?