A deeper look at where each charge unit on this page comes from — the SI-prefixed units used in everyday electrical work, the practical units used for battery capacity, the chemistry and physics units used in electrochemistry and particle physics, and the older CGS units still found in some literature.
SI-Prefixed Coulomb Units (Coulomb through Picocoulomb)
Coulomb, Kilocoulomb, Millicoulomb, Microcoulomb, Nanocoulomb, and Picocoulomb are all the same underlying unit — the coulomb, defined as the charge transported by a steady current of one ampere flowing for one second — scaled by a power of ten. Because every SI conversion is an exact power of ten, there is no rounding error going between any two of these units.
Practical & Battery Units (Ah, mAh, A·s, mA·s)
Ampere-hour and milliampere-hour are the units printed on battery labels, expressing charge as current sustained over an hour rather than a second — 1 Ah equals 3,600 C. Ampere-second and milliampere-second are numerically identical to the coulomb and millicoulomb respectively (since 1 ampere is defined as 1 coulomb per second), included here as alternate labels some datasheets and textbooks use rather than as distinct physical quantities.
Chemistry & Physics Units (Faraday, Elementary Charge)
The elementary charge (e) is the magnitude of charge carried by a single proton or electron — 1.602176634×10⁻¹⁹ C, an exact value under the 2019 SI redefinition. The Faraday constant is the charge of one mole of electrons (Avogadro's number of elementary charges), used throughout electrochemistry via Faraday's laws of electrolysis to relate charge passed to the mass of substance deposited or dissolved.
CGS Units (Statcoulomb, Abcoulomb, Franklin)
These units come from the older centimeter-gram-second (CGS) system rather than SI. The statcoulomb (statC), also called the Franklin (Fr) — the same unit under two historical names — is the electrostatic-unit (ESU) definition of charge, about 3.336×10⁻¹⁰ C. The abcoulomb (abC) is the electromagnetic-unit (EMU) definition, exactly 10 C. Both are largely superseded by SI units today but still appear in some physics literature and historical texts.
This guide is provided for educational and reference purposes. Always confirm measured or specified charge values against a datasheet, lab instrument, or manufacturer documentation before relying on them for any electrical, chemical, or safety-critical work.
