Specify max width for a string in c# [duplicate]

This question already has an answer here:

• Calculate the display width of a string in C#? 6 answers

So I have to manage a listbox that has columns like table and I would like to give each column a fixed width. I wrote this method to convert the strings into a fixed length:

const int nameMaxWidth = 20;
int nameLength = name.Length;

if (nameLength < 20)
{
   while (nameLength < 20)
   {
      name = name + " ";
      nameLength++;
   }
}
else
{
   name = name.Substring(0, nameMaxWidth);
}

but it seems that it does not work since each letter has different size, for example nnnnn is longer than iiiii although both have the same length. I have tried String.Format but it doesnt work either. Is there anything I can do?