someboy knows mybe how to calculate the zoomlevel for the qt map item?
I am displaing pints on the map in a circle of 50km.

I got a circle on the map and want to set the zoomlevel of the map to a point where the circle has a diameter of 80km
so the points on the map fitts to the circle inside.

Here a picture:

Picture of my Map Item

But i cant figure out how the calculation shoud look like.

Somebody got experience in this??

Regards