Several measurements are used to indicate the size of the lens, mainly the base curve and diameter. These are used to represent the actual size or shape of the lens.
Base curve
Base curve measurement indicates how curved the contact lens is. The smaller the baser curve, the more round the front of the lens becomes. Steep lenses are tight on the cornea, so the circulation of tears is not smooth, which can lead to corneal due to lack of oxygen. Flat lenses do not hold the lens of the cornea and keep moving in the eye. But even if the lens is Steep, if the lens is too small for the eye, it is possible for the lens to move without being fixed on the eye. Therefore, it is recommended to wear the correct base curve lenses for wearing comfort.
Diameter
"Diameter" means the diameter of the lens. "Graphic diameter" means the diameter of the part of the color.  "Pupil diameter" means the diameter of the pupil hole (uncolored part).
The common misconception is that if the "Diameter" is the same, it would cover all cornea in the eyes. As described at the picture below, the important thing for the color lenses is actually "Graphic Diameter".
Usually, if the "Diameter" is big, "Graphic diameter" is big. And if the " Diameter" is small, the "Graphic diameter" is small. However, for some special designs of the color contacts, there are exceptions. So if you are looking for a lens that can cover all your eyes, make sure to check the "Graphic diameter".