In the game you find the setting under Settings → Mouse & Keyboard → Sensitivity X and Y.
Set X and Y sensitivity to the same percentage.
Conversion
CS2 to Fortnite Sensitivity
In short: CS2 sens times 3.96. 1.2 becomes 4.8%. For your own value, just edit the sentence below.
How to set it in Fortnite
What changes when you go from CS2 to Fortnite
CS2 turns 3.96 times further per mouse count than Fortnite. That is why the number gets bigger while your mouse distance stays the same.
Fortnite shows 26.3° less field of view than CS2 by default (80° against 106.26°). The picture looks a little tighter and movement on screen a little faster.
In Fortnite you can enter up to 1 decimal place. Use all of them to keep the conversion exact.
Common questions
How do I convert CS2 sens to Fortnite?
Multiply your CS2 sens by 3.96. 1.2 in CS2 becomes 4.8% in Fortnite.
Where do I set the sens in Fortnite?
Settings → Mouse & Keyboard → Sensitivity X and Y. Set X and Y sensitivity to the same percentage.
Why does Fortnite still feel a bit different?
CS2: 90° at 4:3, about 106° at 16:9. Fortnite: Default 80°, check in the game whether you changed it. 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.