I would like to see cm's instead of pixels when using the Image Size tooltip as I am working with large SVG images - I'd like users to determine sizes in cm's. Appreciate this will require some sort of add-on script. Wonder if anyone else has been able to achieve this or can make any suggestions. Thank you.
this is not possible in the backend as it depends not only on the size in cm but also on the dpi. You can use calculators such as http://www.pixelrechner.ch/ (Language german, but there are also lots of websites in english available) in order to get to know the required pixelsize.
Depending on what you would like to get you can predefine some sizes for your users in cm so they don't have to deal with pixel.