When you are in layout-mode you can see a dotted line on the right of your layout marking the boundary for the printable area.
The position of this dotted line is determined by combined result of the paperformat that is chosen in the "print-setup" and margins set in the"Printing-tab" of the "Layout-setup" dialog from the"Layout-menu" in "Layout-mode"
Sorry, I should have been more specific. I am aware of the sizing you mentioned. My question is, if I do not care about printing, and just want a wider layout, how can I speficy the width I want?
You don't, the layout will be as wide as the objects you create on it. So if you want a layout of say 1000 pixels wide, simply create an object (anything from a field to a picture or a button, anything) that has its far right boundary at 1000 pixels from the leftside of the layout, thats all.