There is an IAP app (costs $1) that has a searchable database of many pen kits, including tube lengths. You can run it on iPhone or Android. 
It includes a "Drill Bit Converter" that converts inches (fractions), inches (decimal), mm, and drill gauges. That's useful, but what makes it outstanding is that it will show you the nearest fraction (to a /64th) and drill gauge along with the associated "error". The drill bit converter is worth the cost of the app by itself. 
... for a buck ... take a chance ... Highly recommended!!