Increasing size of Rich Text Editing Control
When using the rich text column type in SharePoint lists the edit control has a fixed width of 384 pixels. This is often too small for easy editing.
The width of the control used to edit rich text is set through the ms-rtelong style. You can change the width using the style in the core.css or other style sheets you may be using. However, this will change the width for every use of this control in your site.
If you need to change the width for a single form, open the form in SharePoint Designer and add a style defining ms-rtelong at the top of the content place holder in which the form is displayed with new dimensions, e.g.
<asp:Content ContentPlaceHolderId=”PlaceHolderMain” runat=”server”>
You can do this for standard uncustomised forms (e.g. NewForm.aspx) or for pages you create using the custom list form web part.