In Coulomb’s law, the constant of proportionality K has the units

$$\begin{gathered} F=K\frac{q_1{q}_2}{r^2} \\ K=\frac{F{r}^2}{q_1 q_2} \end{gathered}$$

Here F is measured in N, r is measured in m, $q_1,q_2$are measured in C

SI unit of K is $N{m}^2/C^2$