The Coulomb constant, the electric force constant, or the electrostatic constant (denoted ke, k or K) is a proportionality constant in electrostatics equations. In SI units it is equal to 8.9875517923(14)×109 kg⋅m3⋅s−2⋅C−2.
The constant of proportionality k is called Coulomb’s constant. In SI units, the constant k has the value. k = 8.99 × 10 9 N ⋅ m 2 /C 2. The direction of the force is along the line joining the centers of the two objects.