We have proposed in one of our former reports a new definition of dot gain for halftone prints. The direct measurement of the ink layer thickness involved in the definition of mechanical dot gain is time and labor consuming, and thus colorimetric measurements are the best way of determining the degree of dot gain from a practical viewpoint. The present report tries to quantify the degree of colorimetric dot gain in terms of the conventional Yule—Nielsen n. By assuming the n value to be constant over the entire visual spectrum, the spectral reflectance of a halftone print is calculated in order to derive the corresponding chromaticity coordinate. The change of the n value with halftone frequency and marking systems indicates that the n value correlates well with the degree of mechanical dot gain estimated from the microscopically observed dot structure. By using n as the measure for dot gain, it is possible to compare the degree of dot gain between prints differing in color saturation.