Gold crystallises in the fcc structure with edge length 408 pm. Its density is (M = 197 g/mol, $N_A = 6.022 \times 10^{23}$):

$\rho = nM/(a^3 N_A)$. fcc: $n=4$. $a = 408\,\text{pm} = 4.08\times10^{-8}$ cm; $a^3 = 6.79\times10^{-23}$ cm³. $\rho = 4 \times 197 / (6.79\times10^{-23} \times 6.022\times10^{23}) = 788/40.9 \approx 19.3$ g/cm³ — matches the known density of gold.