Enter the force between two charges, the magnitude of each charge, and the distance between them into the calculator to determine Coulomb’s constant. This calculator assumes the charges are in a vacuum.

Coulomb’s Constant Formula

The following formula is used to calculate Coulomb’s constant (k):

k = F * d² / (q₁ * q₂)


  • k is Coulomb’s constant (N·m²/C²)
  • F is the force between the charges (Newtons)
  • q₁ is the magnitude of charge 1 (Coulombs)
  • q₂ is the magnitude of charge 2 (Coulombs)
  • d is the distance between the charges (meters)

To calculate Coulomb’s constant, multiply the force by the square of the distance between the charges and divide by the product of the magnitudes of the two charges.

What is Coulomb’s Constant?

Coulomb’s constant is a proportionality factor that appears in Coulomb’s law, which describes the force of attraction or repulsion between two point charges. The constant relates the force between two charges to the product of their charges and the inverse square of the distance between them. In a vacuum, Coulomb’s constant is approximately 8.9875517873681764 × 10⁹ N·m²/C².

How to Calculate Coulomb’s Constant?

The following steps outline how to calculate Coulomb’s constant.

  1. First, determine the force (F) between the two charges in Newtons.
  2. Next, determine the magnitude of charge 1 (q₁) and charge 2 (q₂) in Coulombs.
  3. Next, determine the distance (d) between the two charges in meters.
  4. Next, gather the formula from above = k = F * d² / (q₁ * q₂).
  5. Finally, calculate Coulomb’s constant (k) in N·m²/C².
  6. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Force (F) = 5 Newtons

Charge 1 (q₁) = 1 Coulomb

Charge 2 (q₂) = 2 Coulombs

Distance (d) = 3 meters