In this paper, we propose a calculation model that gives a unique metric-lightness for object-colors, which is independent of different kinds of colorimeters and also matches the actually perceived lightness. Each colorimetric result with different types of measuring geometry, for example, 0/45, d/8(SCI), and d/8(SCE), can be considerably different from others, because of the influence f the component reflected normally from the sample surface. In order to investigate the difference between the actual sensation and each output of measuring geometry, we have made a subjective experiment for many achromatic samples that are composed of various levels of reflectance and those of gloss. As a result, the measured results with d/8(SCE) are shown to be closest to human perception. However, by relating the correlation of gloss to the metric-lightness for any measuring geometry, these differences for the same sample can be decreased.