As a sysop, I've often needed to find an external tool to calculate ranges for range blocks, but there is one that is available within the checkuser interface. I propose that it be made available elsewhere as well, so that non-checkusers can use it too.
(For now, I've hacked together https://meta.wikimedia.org/wiki/User:DannyS712/CIDR.js to load the javascript and display the form at Special:BlankPage/CIDR)