The quantitative description of the size of a display gamut is crucial for designing the wide-gamut display of high saturation primaries. A method to count the discernible colors in a display gamut with the color-difference formula CIE94 is shown. The color difference between neighboring discernible colors in a display gamut is assumed to be unit . The counting result shows that there are 199,491 discernible colors for the ITU-R BT.709 standard display. The number of discernible colors of two wide-gamut LED displays is compared with the standard display, which is more meaningful for representing their relative gamut sizes. For the considered three- and four-primary LED displays, their gamut volumes in CIELAB color space are respectively 1.76 and 1.98 times larger than the standard display. It is found that the number of discernible colors of the two LED displays is only 1.38 and 1.49 times larger than the standard display. The impact of flare on the reduction of the number of discernible colors and gamut volume is shown. The number of discernible colors and gamut volume is respectively reduced by 30%, with about 3.3 and 2.5% flare levels for the three displays considered in this work.