Coulomb’s Law Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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A fast coulomb’s law estimate is valuable only when the setup is clear. Many E&M relationships are simple proportionalities or inverse powers, making a one-input sensitivity check an effective way to catch unit mistakes. The sections below show exactly what this page calculates, how to enter the data, and where the simplified model stops.

What this calculator does

The calculator isolates the relationship between Charge 1 (q₁), Charge 2 (q₂), Distance (r) and repulsive electrostatic force. That makes it useful for testing how one input changes the answer without mixing in unrelated assumptions.

How to use it

Fill in Charge 1 (q₁), Charge 2 (q₂), Distance (r) exactly as defined on the page. Set Charges are… to match the solve path you want. After calculating, change one influential input slightly and confirm that the result moves in the direction predicted by the equation; this is a quick unit and setup check.

How the calculation works

Coulomb force is F = kq1q2/r² with k = 1/(4πε0). The headline shows |F|, while the sign of q1q2 identifies an attractive or repulsive interaction.

Example

With the default setup (Charges are… = Same sign; Charge 1 (q₁) = 1e-06 C; Charge 2 (q₂) = 1e-06 C; Distance (r) = 1 m), the page reports repulsive electrostatic force of 0.008988 N. Once this baseline matches, change only one quantity at a time so you can see which variable is controlling the result.

How to interpret the result

Use the repulsive electrostatic force as the result of the stated electromagnetic relationship. Check whether the output is linear, inverse, inverse-square, or logarithmic before judging how a change in one input should affect it.

Limitations and notes

Real electrical and magnetic systems can add parasitics, finite geometry, temperature dependence, nonlinear materials, frequency-dependent losses, tolerances, and measurement uncertainty beyond the ideal relationship shown here. Before carrying the number into a design or report, confirm Charge 1 (q₁), Charge 2 (q₂), the unit system, and the model assumptions. Extra decimal places do not compensate for an input that represents the wrong physical quantity.