First of all, question How to measure width of character precisely? which is answered, doesn\'t really help for this case, so this isn\'t a duplicate of that.
Try to use this methods:
GDI+ (graphics.MeasureString and graphics.DrawString) >> System.Drawing.Graphics
GDI (TextRenderer.MeasureText and TextRenderer.DrawText)
It also may help you:
Write a custom measure method:
- Split entry string on special characters
- Use above .net methods
- Calculate width of special characters and sum ...
Read Ian Boyd answer