About the Coulomb's Law Calculator
Electric charges push or pull on each other. Like charges repel and opposite charges attract, and the force grows with the size of the charges and weakens quickly with distance. This calculator uses Coulomb's law to give the force between two point charges. Enter the charges with their signs, choose units from coulombs down to picocoulombs and enter the distance. Type the two charges with their signs and the distance and the electric force appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Coulomb's Law Calculator
- 1Enter the two charges with their signs and the distance.
- 2Pick the units or options from the menus if the electric force tool offers them.
- 3Read the electric force in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the electric force
Students use the law in physics and electronics courses. It explains static cling, the shock from a door handle and the forces in dust filters and laser printers. Engineers use it as the starting point for the design of electrostatic devices.
The law has the same shape as Newton's law of gravity, but charges can be positive or negative, so the force can push as well as pull, and it is incomparably stronger: the electric force between two protons is about 10³⁶ times their gravitational pull.
How the electric force is worked out
F = k × |q1 × q2| ÷ r², with k = 8.9876 × 10⁹ N·m²/C². The force is repulsive if the charges have the same sign and attractive if they have opposite signs. Two charges of +1 µC and +2 µC placed 10 cm apart repel each other with 1.80 N. If one is negative (−2 µC), the force is the same size but attractive. At twice the distance, the force falls to a quarter.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Five charge units
- Three distance units
- Attractive or repulsive shown
Mistakes to avoid with electric force
Charges of one coulomb are huge; practical static charges are micro- or nanocoulombs. Take care to enter the sign of each charge, and to choose the right unit. The law holds for point charges or uniformly charged spheres, measured from their centres.
On phone and computer
On a phone, type into the boxes one after another and read the electric force underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the electric force move. The coulomb's law calculator works the same on both. Forces share a pattern. Compare with Gravitational Force Calculator and Force Calculator, and see how charges are stored with Capacitor Calculator and Ohm's Law Calculator.
Features
- Distance is squared
- Use the sign of each charge
- Vacuum or air only
- Clear messages when the electric force inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate electric force?
F = k × |q1 × q2| ÷ r², with k = 8.9876 × 10⁹ N·m²/C². The force is repulsive if the charges have the same sign and attractive if they have opposite signs. Two charges of +1 µC and +2 µC placed 10 cm apart repel each other with 1.80 N. If one is negative (−2 µC), the force is the same size but attractive. At twice the distance, the force falls to a quarter.
What is the formula for electric force?
F = k × |q1 × q2| ÷ r², with k = 8.9876 × 10⁹ N·m²/C². The force is repulsive if the charges have the same sign and attractive if they have opposite signs. The coulomb's law calculator applies it exactly and rounds only the displayed answer to six significant figures.
What is a coulomb?
The unit of charge. One coulomb is about 6.24 × 10¹⁸ electron charges.
Why does the sign matter?
It decides whether the force is repulsive or attractive. The size of the force depends only on the absolute values.
Does the medium matter?
Yes. In water the force is about 80 times weaker than in air or vacuum. This tool gives the value for vacuum or air.
Is this coulomb's law calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.