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Coulomb’s Law Calculator

Enter two charges and the distance between them to find the electric force.

µC

Use a negative number for negative charge.

µC
m

Must be above 0.

This result is an estimate only. Double-check important figures before relying on them.

How it is calculated

  • Convert microcoulombs to coulombs (× 10⁻⁶)
  • F = k × |q₁ × q₂| ÷ r²
  • If the product is negative the force attracts, if positive it repels

To compare with gravity, see the gravitational force calculator.

Worked example

Two charges of 1 µC, 1 m apart:

  • F = 8.9876 × 10⁹ × 10⁻¹² ÷ 1 = 0.0089876 N, repulsive

Why your number may differ

The law applies to point charges, or to charged spheres measured from their centres. A medium other than air or vacuum reduces the force.

Frequently asked questions

What is Coulomb’s law?

The force between two point charges is proportional to the product of the charges and inversely proportional to the square of the distance: F = k × q₁ × q₂ ÷ r².

When do charges attract?

Opposite charges (one positive, one negative) attract. Like charges repel.

What is k?

Coulomb’s constant, 8.9876 × 10⁹ N·m²/C², for charges in a vacuum or in air.

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