They are slightly smaller than your normal 'board game' d6 dice, and they are also considerably lighter. They are also very, very rounded and combined with their light weight, they roll all over the place, spin on a corner, bounce off decks of cards, roll in large circles across the board, and generally never stop rolling around during a throw. If I ever wanted to annoy a gaming group with dice that just do not stop puttering around and taking forever to settle down, I would use these dice.
One took a near-perfect two-foot diameter circle path around our Eldritch Horror game board before bouncing off a deck of cards before stopping. Another spun on its corner for a whole second before flopping around to come to a rest. One had to be caught before it rolled off the table - after it bounced off a deck of stacked cards and rolled right back at me in the opposite direction in which I threw it.
Their light weight means they are less likely to knock over game pieces and push things around, but their silly antics in a way endears me to these dice. Rolling them and seeing how they can annoy or entertain you on the next throw makes them worth the price of admission. They are my my go-to "crazy dice" set.