A font I am using is missing a couple special characters so I made my own. I'm trying to package them together as a typeface using IcoMoon. However without knowing the original font's metrics I can't get the scale right. I might be going about this totally wrong, any suggestions?
Edit: I also have concerns about usage rights considering this is a paid font. To be clear I do not plan to distribute the custom font I am creating, just use it on my site and for print work.