⚡ Coulomb's Law Calculator
Enter two charges and their separation to get the electrostatic force between them — magnitude and whether it attracts or repels.
Force magnitude
0.8988 N
Direction
Repulsive ↕
like charges push apart
Coulomb's law: F = k·q₁·q₂ ÷ r², with k = 8.99×10⁹ N·m²/C². The force is repulsive when the charges have the same sign and attractive when opposite. Charges are in coulombs — use scientific notation for the usual micro- (1e-6) and nano- (1e-9) coulomb values. The field each charge creates at that distance is E = k·q ÷ r². 🔒 In your browser.
How the coulomb's law calculator works
Coulomb's law gives the force between two point charges: F = k·q₁·q₂ ÷ r², where k = 8.99×10⁹ N·m²/C² is the Coulomb constant and r is the distance between them. The tool computes the magnitude and reads the sign of the product q₁·q₂ to tell you the direction — like charges repel, opposite charges attract — and also shows the electric field each charge produces at that distance.
Enter charges in coulombs; everyday charges are tiny, so use scientific notation (1 µC = 1e-6 C, 1 nC = 1e-9 C). The law is the electrostatic twin of Newton's law of gravitation — both fall off as 1/r² — but electric forces can attract or repel and are vastly stronger. It applies to point charges (or uniformly charged spheres) in a vacuum.
Frequently asked questions
What is Coulomb's law?
It gives the electrostatic force between two point charges: F = k·q₁·q₂ ÷ r², with k = 8.99×10⁹ N·m²/C². The force grows with the charges and falls off with the square of the distance between them.
How do I calculate the force between two charges?
Multiply the two charges, multiply by Coulomb's constant (8.99×10⁹), and divide by the distance squared. For two 1 µC charges 0.1 m apart: 8.99×10⁹ × (1e-6)² ÷ 0.1² ≈ 0.9 N.
When is the force attractive or repulsive?
Like charges (both positive or both negative) repel; opposite charges attract. The tool determines this from the sign of the product of the two charges.
How is Coulomb's law like gravity?
Both are inverse-square laws — force ∝ 1/r². But gravity only attracts and depends on mass, while the electric force can attract or repel and depends on charge, and it is enormously stronger for everyday particles.
What is the electric field of a point charge?
E = k·q ÷ r², the force per unit charge a distance r from the charge. Multiply it by a second charge to recover the Coulomb force. The tool shows the field alongside the force.