6 Answers, 1 is accepted
You can handle a server side event of the RadFilter control (e.g. OnFieldEditorCreated) and then when a new expression is added access the field editor (in this case the textbox) and set its proper width.
All the best,Marin
the Telerik team


Have you enabled scrolling on the window? I think the width of the filter is limited by the widow's dimensions. If it has scrolling the filter should extend as much as it is needed and not break the layout.
Regards,Marin
the Telerik team

The pop up RadWindow can enabled scrolling. But the RadFilter will not expand his width and will have a break.
If all the parent containers that hold the filter are set to expand to 100% width and the window is wide enough or has scrolling then the RadFilter should not be limited on its width. Make sure that the above requirement is accomplished and if the problem persists please share the markup declaration of the content of the window so we can check it on our side.
All the best,Marin
the Telerik team