Looks like a 6 deck?
Just measure the length of the compartment between the front plastic and the black insert thing when slid to the back, and then measure the height of a standard deck of cards to see how many decks will fit in there. (Although, if this makes sense, you may need to measure horizontally, not along the upward angle of the clear plastic.) Just eyeballing it, it looks like there should be space for 6 to 8 decks to fit in there.I have no idea