In the game you find the setting under Options → Controls → General → Sensitivity.
Conversion
Rainbow Six Siege to Overwatch 2 Sensitivity
In short: Rainbow Six Siege sens times 0.8681. 10 becomes 8.68. For your own value, just edit the sentence below.
How to set it in Overwatch 2
What changes when you go from Rainbow Six Siege to Overwatch 2
Overwatch 2 turns 1.15 times further per mouse count than Rainbow Six Siege. That is why the number gets smaller while your mouse distance stays the same.
Overwatch 2 shows 11.5° more field of view than Rainbow Six Siege by default (103° against 91.49°). The picture looks a little wider and movement on screen a little slower.
In Overwatch 2 you can enter up to 2 decimal places. Use all of them to keep the conversion exact.
Common questions
How do I convert Rainbow Six Siege sens to Overwatch 2?
Multiply your Rainbow Six Siege sens by 0.8681. 10 in Rainbow Six Siege becomes 8.68 in Overwatch 2.
Where do I set the sens in Overwatch 2?
Options → Controls → General → Sensitivity.
Why does Overwatch 2 still feel a bit different?
Rainbow Six Siege: Slider from 60 to 90, vertical (default 60, about 91° horizontal at 16:9). Overwatch 2: Slider from 80° to 103°. Match the field of view as closely as you can; then the converted sens feels most natural.
Does this also apply to scopes?
No. The values are for hipfire. Zoom and scope sensitivities are set separately in the game.
Should I change my DPI?
No. Keep your DPI and only change the sens in the game. That keeps your feel the same everywhere.