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Coulomb's Law Calculator

Calculate the electrostatic force between two point charges from their charge and separation distance, in metric or imperial distance units.

Electrostatic force
0.008988 N
Interaction
Repulsive (like charges push apart)

How it works

Coulomb's law gives the electrostatic force between two point charges: F = k·|q₁·q₂| ÷ r², where q₁ and q₂ are the charges, r is the distance between them, and k is Coulomb's constant, 8.9875517923×10⁹ N·m²/C² — the current CODATA-recommended value, verified rather than relied on from memory since this site's content bar treats a published physical constant like this the same as a fixed engineering table.

The sign of q₁×q₂ decides the direction, not just the size, of the interaction: two charges with the same sign (both positive or both negative) repel each other, while two charges with opposite signs attract. This calculator reports both the force's magnitude and which of those two cases applies. Charges are entered in microcoulombs (μC) because a full coulomb is an enormous amount of charge — two 1-coulomb charges 1 meter apart would repel with a force of about 9 billion newtons.

FAQ

Why is distance unit-toggled but charge isn't?

Distance is a real-world physical length, so it gets this site's standard metric/imperial toggle. Charge, measured in coulombs, doesn't have a commonly used imperial counterpart the way length, weight, or temperature do, so it's entered in microcoulombs regardless of which unit system is selected.

Does this account for charges moving or a surrounding medium?

No — this is the basic form of Coulomb's law for two stationary point charges in a vacuum (or, to a very close approximation, in air). A charge distributed over a real object, or a dielectric medium other than air between the charges, both change the force somewhat and aren't modeled here.

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