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
Call of Duty to Fortnite Sensitivity
In short: Call of Duty sens times 1.188. 5 becomes 5.9%. For your own value, just edit the sentence below.
How to set it in Fortnite
What changes when you go from Call of Duty to Fortnite
Call of Duty turns 1.19 times further per mouse count than Fortnite. That is why the number gets bigger while your mouse distance stays the same.
The default field of view is almost the same: Call of Duty 80°, Fortnite 80° horizontal. The picture feels alike.
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 Call of Duty sens to Fortnite?
Multiply your Call of Duty sens by 1.188. 5 in Call of Duty becomes 5.9% 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?
Call of Duty: Slider from 60 to 120 (horizontal, default 80). 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.