Coulomb's Law Calculator

Two +1 µC charges 10 cm apart in vacuum push each other away with 0.898755 N, from Coulomb’s law F = kq₁q₂/r².

Solve for:

Electrostatic force FCharge 1 q₁Charge 2 q₂Distance r

Show electrostatic force in:

Charge 1 q₁:

Charge 2 q₂:

Distance r:

Electrostatic force F =

0.89875517923 N

Precision

Full answer, then cut to fewer decimals (not rounded):

0.89875517923 N
0.8987551792 N
0.898755179 N
0.89875517 N
0.8987551 N
0.898755 N
0.89875 N
0.8987 N
0.898 N
0.89 N
0.8 N

In kN: 0.0008987551792 kN
In mN: 898.7551792 mN
In lbf: 0.2020482019 lbf
In kgf: 0.09164752278 kgf
In dyn: 89875.51792 dyn
Interaction: repulsive (like charges)
k = 1/(4πε₀): 8.9875517923 × 10⁹ N·m²/C²

Step-by-step solution

F = k × |q₁ × q₂| ÷ r²
F = k × |0.000001 × 0.000001| ÷ 0.1²
F = 0.8987551792 N

Coulomb's Law Formula

F = k |q₁ q₂| / r²

k = 1/(4πε₀) = 8.9875517923 × 10⁹ N·m²/C², q the charges, r the distance between them

Worked Example

Two +1 µC charges 10 cm apart in vacuum:

F = k × |q₁ × q₂| ÷ r²
F = k × |0.000001 × 0.000001| ÷ 0.1²
F = 0.8987551792 N

In mN: 898.7551792 mN · In lbf: 0.2020482019 lbf · In kgf: 0.09164752278 kgf · In dyn: 89875.51792 dyn · Interaction: repulsive (like charges) · k = 1/(4πε₀): 8.9875517923 × 10⁹ N·m²/C²

Electric versus gravitational force

Between a proton and an electron, the electric attraction is about 2 × 10³⁹ times the gravitational one. Both fall as 1/r², so the ratio does not depend on distance.

Frequently asked questions

What about charges in water or oil?

Divide by the medium’s relative permittivity εᵣ: water (εᵣ ≈ 80) weakens the force about 80-fold, which is why salts dissolve.

How small is the elementary charge?

e = 1.602176634 × 10⁻¹⁹ C exactly. Choose e as the charge unit to work with electrons and protons.

Sources

CODATA Recommended Values of the Fundamental Physical Constants: 2018, National Institute of Standards and Technology .

Last reviewed: 2026-10-15. Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.

Cite this page

APA

Scientific Converters. (2026, October 15). Coulomb's Law Calculator. Retrieved October 25, 2026, from https://scientificconverters.com/calculators/coulombs-law-calculator/

IEEE

Scientific Converters, "Coulomb's Law Calculator," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/calculators/coulombs-law-calculator/