How many electrons are necessary to produce a charge of -1.1 C?

The SI unit of quantity of electric charge is the coulomb, which is equivalent to about 6.25 × 1018 e (the charge on a single electron or proton). Hence, the charge of an electron is approximately −1.602 x 10−19 C. The coulomb is defined as the quantity of charge that has passed through the cross-section of an electrical conductor carrying one ampere within one second. The symbol Q is often used to denote a quantity of electricity or charge. The quantity of electric charge can be directly measured with an electrometer, or indirectly measured with a ballistic galvanometer.

Formally, a measure of charge should be a multiple of the elementary charge e (charge is quantized), but since it is an average, macroscopic quantity, many orders of magnitude larger than a single elementary charge, it can effectively take on any real value. Furthermore, in some contexts it is meaningful to speak of fractions of a charge; e.g. in the charging of a capacitor.