Thank you for the question on the number of tablets the Ten Commandments were written on.
Exodus 20 and Deuteronomy 5 states that the Ten Commandments were written on two tablets. They were written on the front and back of the tablets. The size of the two tablets are unknown.
Since Moses smashed the original two tablets, God told him to make two more tablets. Thus the answer is four tablets with the second set a repeat of the first two tablets.
For further insight and discussion:
https://www.quora.com/How-many-pieces-of-stone-were-the-Ten-Commandments-written-on