The present study provides functions to correlate gamut size across different color spaces including 2D planes - (x,y)
and (u',v') and 3D spaces - CIELAB, CIECAM02 JCh and QMh. All gamut size must be converted to NTSC gamut
ratio before using the functions. As viewing conditions influence 3D gamut ratio significantly, predict 3D gamut ratio in
high precision is not easy. However, the mean values, median values, standard deviations, and confidence intervals can
be predicted accurately. In terms of viewing parameters, we can model them individually under IEC reference condition
successfully, the resulted functions would be a good reference to derive more versatile functions to predict gamut ratio
under complex viewing conditions.