The density of a post-1982 penny is about 7.17 grams per milliliter. That value can be determined from measurements of the density of the zinc and copper in the penny and their percentages.
A penny manufactured after 1982 is made from 2.5 percent copper and 97.5 percent zinc. The density of copper is 8.96 grams per milliliter, and the density of zinc is 7.13 grams per milliliter. The weighted average can be used to find the density of the penny. The density of the copper is found by 0.025 times 8.96, and the density of the zinc is found by 0.975 times 7.13. The sum of those densities is the density of the penny.