Triangular gamut area plots on chromaticity diagrams (e.g., CIE xy or CIE u'v') have long been used in attempts to describe and compare the range of colors that can be produced on displays. This has been done despite the long-established recognition that three-dimensional color gamut volumes in color appearance spaces (e.g. CIELAB or CIECAM02) more appropriately describe display performance. Since three-dimensional color gamut volumes are often difficult to measure and compute, this paper suggests a simple model to estimate color gamut volumes from chromaticity gamut areas, CLO/WLO ratio, peak luminance, and diffuse white luminance for RGB and RGBW wide-color-gamut and high-dynamic-range displays.