The ratio of emu of charge to esu of charge is :

 $$\begin{gathered} 1 esu = 3.335640951\times {10}^{-10} C \\ 1 emu = 10 C \\ \frac{1 emu}{1 esu}=\frac{10}{3.335640951\times {10}^{-10}} \\ \frac{1 emu}{1 esu}=2.99792458\times {10}^{10}\approx 3\times {10}^{10} \end{gathered}$$