Field width setting not taking font size into account?

I added some fields to the user for registration. Two of the fields I added were HOME PHONE and MOBILE PHONE. I set both their database field size to 12 characters and the visible/editable field size to 12 as well. However when the user actually puts a value in the field the field is not wide enough on screen, but is however correct in the limiting of the number of characters it will hold.

Can the visible editing area be fixes so that if you put in 12 characters as the visible and editable constraint that on screen they match. I understand this is tricky and there might have to be a maximum visible width due to column layouts and such. Seems like a fontmetrics issue but not sure.

See attached screen shot.