A regular C cassette box (with the pokey tabs cut out) fits:
- 18 sleeved proxy cards (Pokemon card + copier paper)
- 22 sleeved Pokemon cards
- 40 non-sleeved Pokemon cards
Most board game cards are of the same thickness than Pokemon cards so that’s a good starting point.
If you print rules on the backside of a cover, you can save some space!

I have a 3D printed container that holds my C Cassette card games, it’s a design by JezzaWalker and available from 3 to 11 slots.
I find these a perfect solution for Print and Play board games or other small card games as you can print your own custom spine and cover art to make them easier to find and more consistent when you have a larger collection.
For example, here’s my printed version of Skulls of Sedlec with Pokemon cards in sleeves (for rigidity) in a C cassette case.

