Find the electrostatic force between two point charges and how it changes with distance, using Coulomb's Law.

How to Use the Coulomb's Law Charge Calculator

Enter q₁ and q₂ (either can be negative), choose a shared unit for both, then set the distance between them in centimeters or meters. The force updates immediately, along with a line stating whether the two charges are pulling together or pushing apart.

Coulomb's Law is the electrostatic equivalent of Newton's law of gravitation, and it was worked out around the same era — Charles-Augustin de Coulomb published the relationship in 1785, using a torsion balance sensitive enough to measure forces most instruments of the time couldn't detect at all. The force between two charges comes down to one equation:

F = k × |q1 × q2| ÷ r²

k is Coulomb's constant, 8.99 × 10⁹ N·m²/C² — a fixed proportionality figure that makes the units work out to newtons once charge is in coulombs and distance is in meters. Real point charges are almost never a full coulomb; microcoulombs and nanocoulombs are the practical range for anything you'd actually measure on a benchtop.

Repulsive, Attractive, or Nothing at All

The sign of q1 × q2 decides the direction, not the magnitude of either charge alone. Two positive charges or two negative charges always repel — same-sign charges push apart regardless of how large either one is. Mix a positive and a negative charge and the force flips to attractive. Set either charge to exactly zero and there's no force to speak of, which the calculator reports plainly rather than showing a small nonzero number that isn't really there.

Distance carries an outsized effect on the result, because it's squared in the denominator. Double the separation between two charges and the force doesn't halve — it drops to a quarter of its original value. Move them ten times farther apart and the force falls to a hundredth. That's the same inverse-square relationship gravity follows, and it's the reason static cling and similar effects matter enormously at the microscopic scale but vanish almost entirely across a few centimeters of open air.