Method for evaluating the porosity of the surface of a flat steel product with a Zn-galvannealed protective coating, comprising the following steps: - acquiring in each case a measurement value set of at least 10,000 measurement values for at least 400 parallel aligned measurement tracks in a square surface section of the Zn coating, wherein the surface section in question has an edge length of 1 mm; - determining the mean and the median of the measurement values of each measurement value set in the measuring direction, whereby only those measurement tracks for which the mean is greater than the median are considered to be right-skewed; - determining the mean and the median of the measurement values of each measurement value set transverse to the measuring direction, whereby only those measuring tracks transverse to the measuring direction for which the mean is greater than the median are considered to be right-skewed; - determining the proportion of right-skewed measurement tracks on all measurement tracks in the measuring direction; - determining the proportion of right-skewed measurement tracks on all measurement tracks transverse to the measuring direction; - comparing the proportion of right-skewed measurement tracks in the measuring direction and the proportion of right-skewed measurement tracks transverse to the measuring direction with a limit value of at least 60%, wherein a surface of the Zn coating in which the proportions of the right-skewed measurement tracks both in the measuring direction and transverse thereto correspond at least to the limit value, is considered to be porous, whereas samples in which either the proportion of the right-skewed measurement tracks in the measuring direction or the proportion of the right-skewed measurement tracks transverse to the measuring direction are below the limit value, are considered to be non-porous. - acquiring in each case a measurement value set of at least 10,000 measurement values for at least 400 parallel aligned measurement tracks in a square surface section of the Zn coating, wherein the surface section in question has an edge length of 1 mm; - determining the mean and the median of the measurement values of each measurement value set in the measuring direction, whereby only those measurement tracks for which the mean is greater than the median are considered to be right-skewed; - determining the mean and the median of the measurement values of each measurement value set transverse to the measuring direction, whereby only those measuring tracks transverse to the measuring direction for which the mean is greater than the median are considered to be right-skewed; - determining the proportion of right-skewed measurement tracks on all measurement tracks in the measuring direction; - determining the proportion of right-skewed measurement tracks on all measurement tracks transverse to the measuring direction; - comparing the proportion of right-skewed measurement tracks in the measuring direction and the proportion of right-skewed measurement tracks transverse to the measuring direction with a limit value of at least 60%, wherein a surface of the Zn coating in which the proportions of the right-skewed measurement tracks both in the measuring direction and transverse thereto correspond at least to the limit value, is considered to be porous, whereas samples in which either the proportion of the right-skewed measurement tracks in the measuring direction or the proportion of the right-skewed measurement tracks transverse to the measuring direction are below the limit value, are considered to be non-porous.