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Electrostatics · Forces

Coulomb’s Law & Electrostatic Force Calculator

Calculate electrostatic force, either charge magnitude, or separation distance and identify whether two point charges attract or repel.

Formula shown Runs locally Reviewed Aug 11, 2026
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Equation guide

Two stationary point charges separated in vacuum

Force magnitude

F = k|q₁q₂|/r²

Coulomb constant

k = 8.9875517923 × 10⁹ N·m²/C²

Direction

same signs ⇒ repelopposite signs ⇒ attract
Coulomb’s law

Solve the force between two point charges

Enter positive magnitudes using at most three decimal places; use the sign controls for direction. Displayed results are rounded to at most three decimal places.

F = k|q₁q₂|/r²

Choose the unknown and enter the other three positive magnitudes.

r+q₁+q₂F₁F₂Equal force magnitudes · opposite directions · repulsion

Using the model

Symbols, assumptions and limitations

Interpretation notes

The model treats both charged objects as stationary point charges in vacuum. Charge magnitudes determine force size; their signs determine whether the force is attractive or repulsive. Extended charge distributions, material polarization, and relativistic effects are outside this model.

Worked examples

See the method in practice

01

Two microcoulomb charges

Charges of +2 µC and +3 µC separated by 0.500 m repel with a force of about 0.216 N.

02

Opposite charge signs

Changing the second charge to −3 µC leaves the force magnitude unchanged but makes the interaction attractive.

Questions

Frequently asked

Why are charge signs selected separately?

Coulomb’s magnitude equation uses absolute charge values. The signs are then compared to classify the interaction as attractive or repulsive.

What value of k is used?

The calculator uses k = 8.9875517923 × 10⁹ N·m²/C², corresponding to point charges in vacuum.

Can I use this inside a material?

Not directly. A uniform dielectric reduces the force according to its relative permittivity, which this vacuum model does not include.

Sources & review

Equations and examples are checked against the references below. Results are educational and should be independently verified for safety-critical work.

OpenStax University Physics — Coulomb’s Law

Written by the STEM Hub editorial team · Reviewed August 11, 2026 · Review methodology