Electricity & Magnetism
Coulomb's Law
Electric force between two point charges.
Variables
FN
Electric force
Force between charges
In SI units: kg·m/s²
kN·m²/C²
Coulomb constant
8.99×10⁹
In SI units: kg·m³/(A²·s⁴)
Allowed values: greater than 0
q₁C
Charge 1
First charge
In SI units: A·s
q₂C
Charge 2
Second charge
In SI units: A·s
rm
Distance
Between charges
Allowed values: greater than 0
Derivation
Fundamental law. k = 1/(4πε₀).
Your notes
0/5000
Constants in this formula
Check value
Round inputs run through this page's calculator, with each constant at its tabulated value. Use it to test your own working or a rearranged form. It is a test case, not a real-world example.
- k = 8.988 × 10⁹ N·m²/C² (Coulomb constant)
- q₁ = 2 C (Charge 1)
- q₂ = 3 C (Charge 2)
- r = 4 m (Distance)
Result: F = 3.3705 × 10⁹ N
Other electricity & magnetism formulas with the same quantities
- Electric Potential Energy (Electrostatics) shares Coulomb constant, Charge 1, Charge 2, Distance
- Electric Dipole Field (Axial) (Electrostatics) shares Coulomb constant, Distance
Where this formula is listed
- Electricity & Magnetism formulas, under Electrostatics, alongside Uniform Electric Field, Gauss's Law, Electric Dipole Moment and Electric Flux.
- In the electricity & magnetism list it comes before Electric Field.
- Electricity & Magnetism formula sheet, one of 48 formulas printed with symbol keys and SI units.
- The full formula index, grouped by category and topic.
Common questions
What is the Coulomb's Law formula?
Coulomb's Law is written F = k(q₁q₂/r²). Electric force between two point charges. It belongs to Electricity & Magnetism, under Electrostatics.
What are the units in F = k(q₁q₂/r²)?
In SI units, F is electric force, measured in kg·m/s²; k is coulomb constant, measured in kg·m³/(A²·s⁴); q₁ is charge 1, measured in A·s; q₂ is charge 2, measured in A·s; r is distance, measured in m.
How is the Coulomb's Law formula derived?
Fundamental law. k = 1/(4πε₀). The result is F = k(q₁q₂/r²).