About this tool
The Coulomb's Law Calculator is a free, in-browser electrostatics tool that computes the force between two point charges from F = k·q1·q2/r², using Coulomb's constant k = 8.988×10⁹ N·m²/C². Choose whether to solve for the force, either charge, or the separation, and the result updates live as you edit any field.
Charges can be entered in coulombs (C), microcoulombs (µC) or nanocoulombs (nC) using the per-charge unit selectors, and the separation is in metres with force in newtons. The tool reports the magnitude of the force and labels the interaction as attractive (opposite signs) or repulsive (like signs).
All math happens locally in your browser with nothing sent to a server, so it is safe for classwork and quick lab estimates alike.
Frequently asked questions
What is Coulomb's constant here?
k = 8.988×10⁹ N·m²/C² (equivalently 1/4πε₀). Enter charges in C, µC or nC, separation in metres, and force comes out in newtons.
How is attraction versus repulsion decided?
The sign of the product q1·q2 sets it: like charges (both positive or both negative) repel, opposite charges attract. The force tile shows the magnitude and a label for the direction.
How do I enter negative charges?
Type a minus sign in front of the value and pick its unit. When solving for a charge the tool returns the required magnitude in coulombs; you assign the sign based on whether the force is attractive or repulsive.
Why is the result sometimes in scientific notation?
Electrostatic forces span a huge range, so values below 10⁻⁴ or at or above 10⁶ are shown in exponential form (e.g. 8.988e-5 N) to stay precise and readable.