Converting a row values from metrogrid into a series of list<int>?

In your code

gg = (List<int>)metroGrid1.Rows[1].Cells[x].Value;

You are trying to get a single value from column x in the second row of the grid.

That value happens to be of type Double.

You can't assign a Double to a List (of int or any other type). But you can add the value to the list

Try using a for loop or a foreach loop to step through each of the cells you want and use the gg.Add() method to add the values to the List