Use the registry calculation for best accuracy!
Mouse Sensitivity Calculator and Converter
Total entries w/ special options
For a great collection of info, see Skidushe's excellent thread.
Also check out these instructional videos to get started; One covering the basics, and one covering Monitor Distance in details:
Version 7.1.i (October 15, 2018) - This is a brand new version with support for multi-calculations, see this thread for info!
The old version is available here so you can check if you encounter a bug.
New games: Overkill's The Walking Dead, Zula, Krunker, World War 3, Last Tide, Monster Hunter: World, Ring of Elysium and Shadow of the Tomb Raider.