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Coulomb's Law

Also known as force between two charges · electrostatic force

F=ke q1q2r2F = \frac{k_e \, q_{1} q_{2}}{r^{2}}
sig figs

Worked example: Two 1 uC charges 1 m apart → 8.98755 mN. Press Try an example to run it live, then adjust anything.

Enter your known values, leave one input blank, and solves for the missing one. Tap a variable’s symbol to see what it means, with a typical value. Change any unit and the answer follows.

Constant used: built into this formula, no need to enter
ke=8,987,551,786.2 N⋅m2/C2k_{e} = 8,987,551,786.2\ \text{N}{\cdot}\text{m}^{2}\text{/C}^{2}Coulomb constant

Where Coulomb's Law fits

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Electric Field Strength (E = F/q)

See also

Electric Field Strength (E = F/q): Both use electrostatic force and electric charge.Capacitance (C = Q/V): Both use electric charge.Electric Charge (Q = It): Both use electric charge.Electric Field of a Point Charge: Both use electric charge.Electric Potential of a Point Charge: Both use electric charge.Magnetic Force on a Moving Charge: Both use electric charge.
2 more relatedNumber of Elementary Charges (N = Q/e): Both use electric charge.Work to Move a Charge (W = qΔV): Both use electric charge.
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Coulomb's Law explained

q1q2rFF

In 1785 Charles-Augustin de Coulomb hung a charged sphere on a fine torsion wire and measured how hard a second charge twisted it. The result is the electric twin of Newtonian gravity: the force between two point charges grows with the product of the charges and falls off with the square of the distance. Electricity is by far the stronger force: the electric repulsion between two protons is about 10³⁶ times their gravitational attraction, which is why a rubbed balloon can lift paper against the pull of the entire Earth.

Worked example: two 1 µC charges held 10 cm apart feel F = kₑ × (10⁻⁶)² / (0.1)² ≈ 0.9 N, roughly the weight of an apple, from specks of charge. Enter charge magnitudes here; the sign of the product only tells you whether the pair attracts (opposite signs) or repels (like signs).

Coulomb's Law formula

F=ke q1q2r2F = \frac{k_e \, q_{1} q_{2}}{r^{2}}
Where
  • FF= Electrostatic force (N)
  • q1q_{1}= Charge 1 (C)
  • q2q_{2}= Charge 2 (C)
  • rr= Separation distance (m)
Revised 16 October 2026
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formula.expert. (2026, October 16). Coulomb's Law Formula & Calculator. https://formula.expert/solvers/coulombs-law

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