I use this code to do near enough what you want. I think their are lots of variations on this theme though.

LOCAL loTextBox
LOCAL lnLength
LOCAL lnWidth

loTextBox = ThisForm.Control
lnLength = fsize(lcField, lcAlias)

*!* Work out the width based on the current font.
lnWidth = txtWidth(replicate("w", lnLength), ;
loTextBox.FontName, loTextBox.FontSize) * fontmetric(6, ;
loTextBox.FontName, loTextBox.FontSize) + 2