SharePoint standard functionality does not allow a user to define the width of a column. This is most frequently desired when the list is viewed as a whole, and SharePoint automatically word wraps longer field entries – resulting in a somewhat disjointed view display.
Such as the Title and Status fields in the below screen shot:
A simple workaround to this it edit the field name to be longer, however entries of space values are automatically stripped out by SharePoint so just adding spaces after the name doesn’t achieve the desired result.
Underscores will work nicely but are somewhat unsightly. The other option here is to enter “hard spaces” (or non-breaking spaces). Hard spaces are not stripped out by Sharepoint and are achieved by holding down the alt key and entering “0160” on the numeric section of the keyboard.
In order to enter a series of these you can enter the first in another application such as Notepad and copy and paste it as many times as required, then copy the series of hard spaces into the SharePoint list column value.
The result looks like the below with both the Status and Title columns having been increased:
It is a little bit fiddly but does present a simple option for those not wanting to edit the list through SharePoint Designer.