# Step 4-C: Computation of the Gain for a Single Direction

The antenna gain GP at point P is the quotient of the actual field strength and the field
strength of the isotropic radiator at point *P*:

$$G=\frac{{\left|{E}_{ant}\right|}^{2}}{{\left|{E}_{iso}\right|}^{2}}=\frac{{S}_{ant}}{{S}_{iso}}$$