As noted on the side, each of these cartons holds a dozen identical cards with one particular toy. It also states the full item number for the card in question, in this case No. 1168/12 for the Nova Rocket.
9 1/4 in
6 3/8 in
4 1/8 in
It later transpired that my example above would seem to be an odd-one out in having the content information printed on one side. All other Spacex shipping boxes I've seen since have this information printed on their lid.
Because my example has much neater printing, it may be a later example of better quality. Having the information printed on the side would be an improvement, in being much more useful when the boxes are stacked together on a shelf.
The boxes below would likely all be earlier examples, printed in a variety of styles. Although all these boxes hold 12 blister cards of identical length and width, the difference in height of the toys means that some needed much wider boxes than the others.
The two sizes of box shown together
No. 1159/3 Helicopter P3
No. 1161/5 Supply Force Mercury
No. 1165/9 Explorer MEV2
No. 1167/11 Base Patrol Cricket
The MEV2 box again, showing contents
note: an eBay seller in Canada told me of re-used shipping boxes holding 48 cards each: they had been turned inside out and re-taped, so the original printing was on the inside. This printing included Playskool (a Hasbro brand which Triang also marketed outside the US) and Triang-Meccano (used for model trains) with "Toronto, Ontario" now on the inside, and a Spacex model name with the number 48 marked on the outside.