Coulomb’s Law Calculator

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Enter your values after choosing the type of calculation in the tabs. The result updates as you type; press Calculate to confirm and jump to the result on mobile. Use Share to send the calculator with your result.

Coulomb’s law

F = k · |q₁ · q₂| ÷ r² k = 1 ÷ (4πε₀) ≈ 8.9876 × 10⁹ N·m²/C²

The force between two point charges is proportional to the product of the charges and inversely proportional to the square of the distance. Like charges repel and opposite charges attract. In a material, divide by its relative permittivity εᵣ.

Example: 2 μC and −3 μC, 0.5 m apart in vacuum: 8.99 × 10⁹ × 6 × 10⁻¹² ÷ 0.25 = 0.216 N, attractive.

Units and prefixes

Unit	Value
mC (millicoulomb)	10⁻³ C
μC (microcoulomb)	10⁻⁶ C
nC (nanocoulomb)	10⁻⁹ C
Elementary charge e	1.602 × 10⁻¹⁹ C
ε₀ (vacuum permittivity)	8.854 × 10⁻¹² F/m

Constants: NIST CODATA.

Inverse-square law

Doubling the distance cuts the force to a quarter; halving it makes the force four times larger. That’s the same inverse-square form as Newton’s law of gravity, but the electric force is vastly stronger: between two electrons it’s about 10⁴² times their gravitational pull.