SI Units

Coulomb

Definition

The SI unit of electric charge, defined as the charge transported by a current of one ampere in one second (1 C = 1 A·s), equal to the charge of approximately 6.242×10¹⁸ elementary charges.

Explanation

Named after Charles-Augustin de Coulomb. A standard AA battery holds roughly 9,000–10,000 coulombs of charge. The elementary charge of one electron is 1.602×10⁻¹⁹ coulombs — meaning one coulomb represents about 6.24 billion billion electrons. Phone battery capacity is measured in milliamp-hours (mAh); a 3,000 mAh battery stores 3 A × 3,600 s = 10,800 C.

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RELATED TERMS

Meter

The SI base unit of length, defined as the distance light travels in 1/299,792,458 of a second.

Kilogram

The SI base unit of mass, defined by the Planck constant.

Second

The SI base unit of time, defined by the cesium-133 atom.

Kelvin

The SI base unit of temperature, starting at absolute zero.

Ampere

The SI base unit of electric current.