Size is as-packaged, or the diameter of loose marbles. ("D" is the diameter of round items other than marbles.)
The eye-grabbing marbles in this themed net are black swirled with a slate blue, with a frosted finish that makes the marbles easier to control in a game. You get 25 marbles with a shooter packed in a net with a header card printed with colorful graphics and marble game rules.
This etched or "frosted" marble is way better looking in person than in the pics. They have lots of character and a wide variation in color patterns. Out of the 1000+ Mega's that I have my favorite individual marble of the whole collection is a Tarantula.