I'm always a bit rusty when i start building reports in Reporting Services after a while. One thing i always has to figure out is how to set up the page size, body and margins. In a article on Microsoft you can find more information about this subjct. You can set the properties in the properties window or you can set the properties with report properties window (Menu -> Report -> Report properties). The relation between page, body, header and footer looks conceptual like the diagam below.
Below you can see how i manually set the page size of the report with A4 paper settings.
The formula of setting the PageSize Width, bodysize and margins is this: Page Width = Body Width+ Left margin + Right Margin. In my case 21= 19+1+1.
In case of the height of the report you need to set the pagesize. In case of A4 : 29,7cm. In case of the body height you can set whatever you wan't. By setting the PageSize Height property the height of A4 is maintained and when the body height is larger than the pageSize (minus top margin and bottom margin) more pages are displayed/printed.
It's also possible to set the properties with the report properties window. Below you can see an example in inches.
We end up with the follow values for the proprties: