Coulomb’s Law Calculator

How it is calculated

Coulomb's law gives the force between two point charges: F = k × q₁ × q₂ / r², with k = 8.9875 × 10⁹ N·m²/C². Enter the charges q₁ and q₂ in coulombs (C) and the distance r in metres; the force comes out in newtons, printed in scientific notation such as 5.992e-1 meaning 0.5992. The sign matters: charges of the same sign give a positive force (repulsion) and opposite signs give a negative force (attraction). The distance must be greater than zero. The tool assumes point charges in vacuum or air, so a dielectric material reduces the real force.

Common mistakes

• Typing microcoulombs (µC) as if they were coulombs; 2 µC must be entered as 0.000002 (2e-6).
• Entering the distance in centimetres instead of metres, which makes the force 10,000 times too small.
• Forgetting that distance is squared, so halving the distance quadruples the force.
• Ignoring the sign: a negative result means attraction, not an error.
• Applying it to large, extended objects or to charges inside a dielectric without correcting for the medium.