Coulomb’s law calculator


How to use our Coulomb’s law calculator?

Our Coulomb’s law calculator allows to automatically get the force from the Coulomb’s law equation. Indeed, to get this Coulomb force, you only have to define the value of the two charges and the distance between these two charges. These 3 variables are as default in SI unit, but you can change them by clicking on the arrow next the each unit.

The result of the Coulomb’s law formula is also in SI unit, but you can also change them by clicking on the arrow next to the unit of the Coulomb force to get the value in another unit.

The Coulomb’s constant doesn’t have to be specified, it is indeed defined by the calculator.

Table of contents:

Coulomb’s law

The Coulomb’s law (also called the Coulomb’s inverse-square law) defines in electrostatic the force between two electrically charged particles. The electric force between the charged bodies at rest is called the Coulomb force (also called the electrostatic force).

This law is named after the French physicist Charles-Augustin Coulomb, who indeed enunciated it in 1785. The Coulomb’s law is the basis of the electrostatics. This law can be stated as:

“The intensity of the electrostatic force between two electric charges is proportional to the product of the two charges and is inversely proportional to the square of the distance between the two charges. The force is carried by the line passing through the two charges. “

Coulomb’s law formula

The definition of the Coulomb’s law is expressed by the following formula:

F = ke .q1.q2 / r²


  • F is the Coulomb force (Newton). A positive force implies a repulsive interaction, whereas a negative force implies an attractive interaction
  • ke is the Coulomb Constant (8.987551792314 * 109 N.m²/C²)
  • q1 is the charge of the first particle (Coulomb)
  • q2 is the charge of the second particle (Coulomb)
  • r is the distance between the two charges (Meter)


The Coulomb force or electrostatic force is defined by the SI unit of the Force, which is the Newton.


The Coulomb force is expressed by the SI unit Newton, which is symbolized with N.

Coulomb’s constant

The Coulomb’s constant (also called the electric force constant or electrostatic constant) is the proportionality factor that appears in the Coulomb’s law. The constant is defined from the vacuum electric permittivity (also known as the electric constant).

The symbols use for this constant are ke, Kc or k0 while the SI unit expression of this constant is N.m²/C². The recommended value (CODATA) of this constant since its redefinition in 2019 is 8.987551792314 * 109 N.m²/C².

Limitations of Coulomb’s law

The Coulomb’s law is only valid if the three following conditions are fulfilled:

  • the charges have a spherical symmetric distribution
  • the charges are distinct points and they don’t overlap
  • the charges are stationary

These three conditions are also defined as the electrostatic approximation.

Other calculors in this category