Plot zoom panel size from API?

Is it possible to get the current size of the zoomed plot panel in Rstudio automatically? via the API maybe? I had a look in the package vignettes but couldn't see anything that looked relevant.

Currently I am right-clicking the panel and inspecting it to get the pixel size then manually copying them to translate into mm. Can I get this information in a more programmatic manner?

What about saving the plot to a file on disk ( Using those functions you can specify some units and then use code to do something with the picture generated. (I hope answered the right question.)

Thanks for the thought @MikeBadescu but what I'm trying to do is work out the size I want an image prior to saving it to disk and hoping to tap in to the convenience of resizing an image in the zoomed plot panel.