Wikipedia says there are 124 states party to the Rome Statute and there are 193 sovereign states that are members of the united nations. Thats 64%, which is most countries.
The State of Palestine is a State Party of the Rome Statute but only a non-member observer state of the UN, so treating the parties to the Rone Statute as a subset of the UN members is not quite right.
Wikipedia says there are 124 states party to the Rome Statute and there are 193 sovereign states that are members of the united nations. Thats 64%, which is most countries.