The precision specifier controls the number of significant digits or zeros to the right of a decimal:

   
  
using System;

public class FormatSpecApp {
    public static void Main(string[] args) {
        int i = 123456;
        
        Console.WriteLine("{0:C5}", i);
        Console.WriteLine("{0:D5}", i);
        Console.WriteLine("{0:E5}", i);
        Console.WriteLine("{0:F5}", i);
        Console.WriteLine("{0:G5}", i);
        Console.WriteLine("{0:N5}", i);
        Console.WriteLine("{0:P5}", i);
        Console.WriteLine("{0:X5}", i);
    }
}