Coulomb’s Law Calculator
Coulomb’s law estimates the electrostatic force between two point charges in vacuum. Charge signs indicate whether the interaction is attractive or repulsive.
How to use this calculator
- Enter both charges in microcoulombs and their separation in metres. The signed force and magnitude are both shown.
- Check the labels and units before applying the result to a real task.
- Change one input at a time when comparing scenarios.
Formula and method
F = kq₁q₂/r², with k ≈ 8.98755×10⁹ N·m²/C²
- F = kq₁q₂/r², with k ≈ 8.98755×10⁹ N·m²/C²
- The point-charge approximation ignores nearby materials, dielectric properties, charge distribution and external fields.
Worked examples
Worked example
Charges +1 µC and −1 µC are separated by 0.1 m.
The signed force along the line joining the charges is about −0.899 N, indicating attraction under the chosen sign convention.
The signed force along the line joining the charges is about −0.899 N, indicating attraction under the chosen sign convention.
Understanding the result
Coulomb’s law estimates the electrostatic force between two point charges in vacuum. Charge signs indicate whether the interaction is attractive or repulsive.
The point-charge approximation ignores nearby materials, dielectric properties, charge distribution and external fields.
Important notes
The point-charge approximation ignores nearby materials, dielectric properties, charge distribution and external fields.
Displayed values are rounded for readability; retain appropriate precision when continuing a calculation.
Frequently asked questions
Which charges attract each other?
Opposite signs attract and like signs repel under the usual electrostatic convention.
Why must the distance be non-zero?
The inverse-square formula divides by distance squared and does not describe coincident point charges.
Does surrounding material affect the result?
Yes. A dielectric medium changes the force compared with the vacuum constant used by this simplified calculator.
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Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.