We'd first want to clarify that the dimensions don't determine how many items you can send in, as you pay up front for a pre-numbered amount of items to be converted.
Additionally, you don't necessarily have to use our box! If you have too many items to fit in our box, or it's too big for the few items that you have, you are welcome to use another box. The most improtant thing is that you use our shipping label, barcode labels, and send everything in one box.
In regards to the dimensions, our boxes are: 17.5" x 12" x 6.5"
The dimensions is the same regardless of the amount of items the box is for!