DPI and CS2 sensitivity
CS2 combines your mouse's configured DPI with the game's sensitivity and other input settings. DPI alone cannot tell you how fast your aim will move.
Use eDPI for simple comparisons
For a basic same-game comparison, multiply DPI by CS2 sensitivity. This gives a convenient eDPI number, although physical cm/360 remains useful when comparing movement requirements.
Example
At 800 DPI and 1.0 sensitivity, the simple eDPI value is 800. At 400 DPI and 2.0 sensitivity, it is also 800. Those configurations can therefore be compared on the same eDPI scale within the same game's conventions.
Check your actual DPI
The manufacturer's configuration software is the authoritative place to see the configured hardware DPI. The browser analyzer on this site can provide an independent estimate when you want to check whether the pointer behavior matches your expectation.
Build a repeatable setup
Record DPI, sensitivity, resolution, Windows pointer settings and mousepad conditions. Change one variable at a time and use repeatable aim drills rather than a single match to judge a change.