That website is a good starting point. It gives maximum COAL (Cartridge OverAll Length), though. The actual desired COAL varies with the caliber, bullet weight, profile, and composition. If you really get into handloading, you can even tailor the length to a specific firearm.
I prefer to make cartridge pens that meet SAAMI (Sporting Arms and Ammuninition Manufacturers' Institute) specs. That is, if you took the cartridge off the pen, it would actually chamber in a matching caliber gun. I even take into account the amount I remove from the tip of the bullet when drilling.
Regards,
Eric