You're likely referring to Mount Vesuvius, which is a volcano, not a crater.

Mount Vesuvius doesn't have a "width" in the same way a crater might. It's a cone-shaped mountain, so it has a base diameter, which is the widest part.

The base diameter of Mount Vesuvius is approximately 4.5 kilometers (2.8 miles).

Let me know if you have any other questions about volcanoes!