So you want the font to resize itself to fit the string in a label?? The method doesn't exist. You'll have to code this up yourself.
I did this (a long time ago!) by creating my own control, inherited from Panel, not Label, and drawing the text myself.
You'll need to use MeasureString
] and the StringFormat options to tell you how big the box is that can contain the drawn string. The font size you pass to MeasureString would be fixed and not ever change. In my code I think I used like 72 points.
You then take the returned size and create a Bitmap with it, then draw your string to the bitmap using the exact same options you passed to MeasureString. When you draw your text, draw the bitmap image (NOT THE STRING!) to your control surface and scale it down to the size you need. Since you're now drawing a picture of your text, and scaling it down, this will, of course, wreck the nice anti-aliased edges of the glyphs drawn.