# Statcoulomb

In physics, a **statcoulomb** (symbol **statC**), formerly known as **esu of charge**, is the unit of electric charge in the cgs-esu (centimeter-gram-second electrostatic system) of units.

By definition, a point charge has magnitude one statcoulomb if it repels a point charge of equal magnitude at a distance of 1 centimeter with a force of one dyne.

- 1 statC = 1 esu of charge = C/(10⋅
*c*) ≈ 3.335 640 95⋅10^{−10}C

where C (coulomb) is the SI unit of charge and *c* is the SI speed of light (*c* ≈ 3⋅10^{8} m/s).

## Conversion to coulomb

The conversion of statC to C can be done as follows. Write

- 1 C =
*k*statC,

and compute *k*. Consider two charges of 1 C each, 1 m apart, then the force between them is according to Coulomb's law in SI units,

(see electric constant for the SI value of ε_{0}).
The same system of two charges has in cgs units a force in dyne (1 dyn = 10^{−5} N):

where we applied Coulomb's law in electrostatic units. Hence