If you are referring to the column width in a list view or in a grid portlet that is easy for a string field, but you may not like the solution.
First you set the column width as big as you need. Then you enter a string value for that field for a record which is as long a as you want and does not have any breaks. That is the only way I know of to force the column width.
The way CA PPM works is the width in field definition determines how much data the column can handle.
The rest is automatic. The column with depends on the "length of data" in each column in the records on one page of a view. Then the space in the browser window is divided between all the columns to give the best fit.
A column with more data gets more space than a column with less data.