Looks like 2 1/2 inch diameter, each section 1/2 an inch, clear resin with a shallower middle ring.
1/2 outer ring + 1/2 inch middle ring (the moat) + 1/2 inch center +1/2 inch middle ring (the moat) + 1/2 inch outer ring = 2.5 inch diameter total.
Depending on lighting, the middle ring may be shallower or thicker than the center and outer ring