Thanks to open source initiative dDDirect, we have a handy and practical way to accurately anticipate the inflated size of a tire on a given rim. Without this or an actual trial fit, the same size tire can vary over 10mm in diameter, mounted to different rims.
This is a critical industry challenge, largely ignored at the present but confusing the performance of highly engineered bikes and wheel systems. See our library for a complete explanation of the system and these issues.
The tool is a sturdy plastic scale, 5.25″ long by 3.5″ wide.