how to get byte size of type in generic list?

I have this generic list and I want to get the byte size of the type like if T is string or int etc., I tried both ways as written in getByteSize(), and just to let you know I am using only one way at a time ...

but when I try to compile, it gives an error saying "Error: The type or namespace name 'typeParameterType' could not be found (are you missing a using directive or an assembly reference?)"

public class iList<T> : List<T> 
    { 
        public int getByteSize ()
        {
            // way 1
            Type typeParameterType = typeof(T);
            return sizeof(typeParameterType);

            // way 2
            Type typeParameterType = this.GetType().GetGenericArguments()[0];
            return sizeof(typeParameterType);
        }
    }

And idea what I am doing wrong here?