How to expand SharePoint 2013 list column size

Steps :-

1. Put the JQuery library file into somewhere can be referenced. In this case, as it will be used by SharePoint Intranet, I have decided to put in the Shared Documents where all SharePoint Intranet users can access.

2. Edit Page (require at least Web Designer permission).

3. Add the Script Editor web part and make it hidden. Then inject below code, note you will need to adjust the column name and URL to match your need.

<script src="https://intranet.rmagroup.net/Shared%20Documents/jquery-2.1.3.js"></script>

<script language="javascript">

   _spBodyOnLoadFunctionNames.push("AdjustColumnWidth");

   function AdjustColumnWidth() {

      $("div.ms-vh-div[DisplayName='Source']").attr("style", "WIDTH: 150px;");

      $("div.ms-vh-div[DisplayName='Priority']").attr("style", "WIDTH: 100px;");

      $("div.ms-vh-div[DisplayName='Description']").attr("style", "WIDTH: 500px;");

      $("div.ms-vh-div[DisplayName='Comments']").attr("style", "WIDTH: 100px;");

   }

</script>