In this letter, a parametric analysis of the Fresnel-field antenna measurement method is performed for a square aperture. As a result, the optimum number of Fresnel fields for one far-field point is guided as $M_{opt}=N_{opt}=D^2/{lambda}R+5$, where D is the antenna diameter, ${lambda}$ is the wavelength, and R is the distance between the source antenna and the antenna under test. For the aperture size 5 ${leq}$ $L_x/{lambda}$ ${leq}$ 20, the tolerable distances for gain errors of 0.5 dB and 0.2 dB can be guided as $R_{0.5;dB}$ ${approx}$ $1.2Lx/{lambda}$ and $R_{0.2;dB}$ ${approx}$ $2.0L_x/{lambda}$, where $L_x$ is the lateral length of the square aperture. The tolerable distances for 20 ${leq}$ $L_x/{lambda}$ ${leq}$ 200 are also proposed. This measurement guideline can be fully utilized when performing the Fresnel-field antenna measurement method.