# Why is a Coulomb the charge of $6.24 \times 10^{18}$ electrons? [duplicate]

Where does the $$6.24 \times 10^{18}$$ number come from? How was it historically derived?

I know that $$1$$ C $$=$$ $$1$$ A s but that just pushes the question down another step, and another and another, at some point where do these numbers actually originate and bubble up from?

• Would this be better on HSM? – Aaron Stevens Sep 12 '19 at 23:12
• Possible duplicate of Definition of Ampere – jacob1729 Sep 12 '19 at 23:15
• Well, apart from the historic conventions, the number stems from the value of the (low energy) electromagnetic coupling constant. It is one of the dimensionless parameters that we simply measure and can't predict using the current best framework of particle physics which is known as the standard model. – Dvij Mankad Sep 12 '19 at 23:34
• I believe that the coulomb (actually a small fraction of it) was originally defined as the charge supported by a typical ball of sulfur, at the time Coulomb made his experiments. But I may be wrong. – Cham Sep 12 '19 at 23:59