Coulomb's Law Calculator

It describes the force between two point charges as F = k times the absolute value of q1 times q2, all divided by the square of their separation r. The constant k is about 8.9875 x 10^9 N m^2 / C^2. The force acts along the line joining the charges.

Charges with opposite signs pull toward each other, and charges with the same sign push apart. The calculator reads the signs you type and labels the result attractive or repulsive, while the force number itself is always reported as a positive magnitude.

Enter charge in coulombs and distance in metres to get force in newtons. Because everyday charges are tiny, use scientific notation such as 1e-6 for a microcoulomb, 1e-9 for a nanocoulomb, and 1.6e-19 for a single electron.

The force depends on 1 divided by r squared, so a separation of zero would give an infinite, unphysical result. The tool rejects zero or negative distances and asks you to enter a positive value.

When the magnitude lands between 0.001 and 10 million newtons it is shown as an ordinary decimal to six significant figures. Outside that band the result switches to scientific notation, for example 3.59500e-4 N, so the value stays readable.

The default constant assumes a vacuum or air, which is very close to it. Inside a material you would divide by the relative permittivity of that medium, which this tool does not apply, so treat the answer as the free-space force.

Both follow an inverse-square law, but electrostatics is enormously stronger for typical charges. The force between two one-microcoulomb charges a metre apart is about 0.009 newtons, vastly more than the gravitational pull between the same two small objects.

This calculator handles one pair at a time. For several charges, compute the force from each pair separately and add the results as vectors, since real forces have direction as well as magnitude.

Yes. Every calculation runs locally in your browser and nothing is sent to a server, so the charges and distances you test never leave your device.