How this calculator works
Each added electron contributes -e coulombs. Dividing the negative of net charge by the exact elementary charge gives an equivalent excess count. A measured macroscopic charge need not be an exact multiple at its measurement precision, so charge-to-count mode preserves the unrounded equivalent value. Count-to-charge mode accepts integer counts up to 9007199254740991 in magnitude.
Formula
Q = -N e and N = -Q/e, where e = 1.602176634e-19 C exactly in SI.
Worked example
A net charge of -1.602176634e-18 C corresponds to 10 excess electrons. Adding 20 electrons gives -3.204353268e-18 C.
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Frequently asked questions
Why does a positive charge give a negative count?
A positive object lacks electrons. The sign here counts added electrons, so a deficit is negative.
Can I enter part of an electron?
Charge measurements can give a fractional equivalent count. Enter an integer when specifying a physical number of electrons.
Are very large counts exact?
Not necessarily. Floating-point charge division is approximate, and integer input is restricted to the safe integer range.