F = k {( |q1|*|q2| ) / R2 }

Where F is the electrostatic force of attraction or repulsion between two charged particles (point charges).
q1 and q2 represent the point charges, which may be negative or positive.
R is the separation between the two points.
k is a constant, where k = 8.99x109 (N*m2)/C2 (Newtons)(meters squared) over (Coulombs squared)

Note the similarities Coulomb's Law and Newton's Law of Gravitation