One of the first things you may notice when creating new reports in Power BI, especially if converting existing reports from other BI tools to Power BI, is that the canvas (page) size is relatively small. In many cases it is too small to hold all the visualizations, slicers, text and headers you want to include. This is by design I think, where the intent is to keep the number of visualizations and information on a report page to a focused set. However, you may find that the default settings are a bit too small. You can customize the canvas size as follows:

In the Report view, make sure that no visualizations are selected (click on a blank area on the report page if necessary). Go to the Visualizations pane.

Click the Format icon. Then expand the Canvas settings section. There you can choose Custom from the Type dropdown, and set your desired custom Height and Width for the canvas area.

Note: If you have not upgraded your Power BI Desktop in the last few months, the Visualizations pane and Format icon may look a little different.

Thanks for reading. I hope you found this useful.