GraphicsPath.AddString vs Graphics.MeasureString

[C# Programming]

hi

why does this fonction don't retrieve the same result as Graphics.MeasureString ?

public RectangleF MeasureString (string str,Font f)
{
using (GraphicsPath gp = new GraphicsPath())
{
gp.AddString(str,f.FontFamily,(int)f.Style,(300 / 72) * f.Size,new Point(0,0),new StringFormat()); // i'm using 300 dpi
return gp.GetBounds();
}
}