# How to deduce the charge of an electron from the charge of an oil drop in the Millikan experiment?

In the Millikan experiment we measure the charge of one oil drop. But how can I measure charge of one electron when I’m not sure how many electrons are contained within one oil drop?

I think the key was that when you measure enough oil drops, you will notice that the charge is always a discrete multiple of some number. So it shows that charge is quantized. With enough data points, you'd see that the smallest charge difference possible is about $1.6\times 10^{-19}$ coulombs.