If you're using Tableau Desktop to create dashboards, device layouts are another approach to creating a dashboard that will work for a variety of browser window sizes. In addition to being different sizes (desktop, iPad, mobile), each layout can contain different items. See Create Dashboard Layouts for Different Device Types for details.
Set overall dashboard size
To set the overall size of a dashboard:
Group items using layout containers
A layout container is an optional way to keep views and objects together. It helps groups of items resize and change position when users interact with your dashboard so that the dashboard doesn't include white space that you don't want.
The image below shows how a dashboard behaves when two views are placed in a vertical layout container versus how they behave when they are not placed in a layout container. Notice how, in the dashboard that uses a layout container, the views adjust vertically as different filters are applied.