There doesn't appear to be anywhere, that I can tell, that indicates how much a Plank Pallet is able to hold. This is the case for viewing the description of the Pallet in the crafting menu, and when viewing the pallet after it's already been built. This information might be handy to have for players in case they want to carefully plan how many they will need/want. 

https://imgur.com/VNnLsJh

i don't see a need for this myself,  if the pallet gets full, build another, they're super cheap material wise and easy to build.  got too many?  break or recycle it, you can always use the recovered materials for other things.

This would be nice to have but it is easier to just count it because each plank pallet holds 24 I believe