You can manually resize the box (assuming you have room for it) by just computing the desired width in twips (1440/inch) and then reloading the box's .Width property (which is in twips). However, you can
easily compute the size
only with non-proportional fonts e.g. Times New Roman as the most common example, or Lucida Console as popular alternative. With non-proportional fonts, the string length in characters times the width of a character in that font gives you the answer, though I don't recall that two different non-proportional fonts are uniform in width for the same font size. Even the difference between normal and bold or normal and italic can complicate the works.
Many people use proportional fonts like Arial or Bookman Old Style as a matter of aesthetics, and there the sizing issue becomes much trickier. Individual character widths are not uniform so you cannot just multiply characters times font width. Routines exist in Excel that can determine the visible length of a string in a particular proportional font (face & size). Native Access doesn't have such a function. You would need to bring in the Excel library among your references to use the appropriate function in Access.
I understand any solution will be very complicated, but here's hopin'... I have a need to sort a column of text strings (basic ASCII characters only) by their printed width in a given font. Opt 1: Range.Autofit works but is not very accurate. Opt 2: ??? Opt 3: It looks...
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The problem is when you deal with proportional fonts, the pixel width isn't easy to determine, particularly if kerning is in force, since in that case you need to know if it has occurred, and if so, how many times. Kerning, if you weren't sure, is the ability to slightly overlap letters when their serifs don't touch, so they take up less space than you might have expected.
Now if you don't care about a little non-uniformity of your text box when using proportional fonts, you COULD just center the text in the box and then compute it as number of characters times the width of the widest character in that font (which you might have to look up or measure.) In cases with lots of L and I (like Williams, e.g.), the name might have a little extra blank space at the ends vs. other names with the same number of characters, and I won't swear that the centering will be perfect either if the kerning was concentrated at one end or the other.