Size is as-packaged, or the diameter of loose marbles. ("D" is the diameter of round items other than marbles.)
These are very impressive agates, just like the banded Carnelian Agates that were so prized in the heyday of marbles. Alternating band carnelian agate alternate with thin lines of white or sometimes black, usually resulting in the classic bull's-eye design. If you are luck you will get patterns that look like chevrons or butterflies! You will not be sorry you bought these!