How many ml of isopropyl are present in a 70ml bottle of rubbing alcohol?

Assuming it is 90% by volume isopropyl alcohol, then 70 ml of rubbing alcohol would contain 63 mls of isopropyl alcohol.

Rubbing alcohol is a mix of water and isopropyl alcohol. How much of a bottle is alcohol and how much is water depends on the strength of that bottle. Some is 50%, some 90%.