Sizing Input fields

I want to be able to size the date portion of a field.
For example,
First Name is 30 characters
Last Name is 50 characters
Area Code is 3 characters

I would like to make the input box as wide not not wider
than the total amount of characters. Area code is 3 character
so I would like a box that is 3 characters.

Please let me know.

Thanks.
Les
lcorzberg