Go to this third-party webtool: https://jscalc.io/embed/za5TQmMatqU4kXSR
If you feel safer, google "mouse sensitivity calculator" and one of the top links will go to a URL at JSCalc.io and will be titled "Mouse Sensitivity Calculator". This should take you to the same URL posted above.

On the third-party webtool:

1. Set the game to "Hunt: Showdown".
   
2. Set "Sensitivity Units" to "Virtual" and leave "Virtual Unit" at "Game Sensitivity Value".
   
3. Input your desired game sensitivity value. This value is the "Default" sensitivity in-game.
   You may instead prefer to find a desired ADS sensitivity (iron sight) in-game first, then input a default sensitivity into the webtool until the web tool's ADS sensitivity in the first table on the right matches your desired ADS in-game sensitivity. If you prefer this method, do it at the end of these steps (after you have filled everything else out).
   
4. Leave "Zoomed Mouse Sensitivity" section alone: leave "Unit of Measurement" at "Visuomotor" and "Match Hipfire's Visuomotor".
   
5. Unless you are using the default Field of View, set "Field of View" to custom. Don't insert your in-game FoV here. That's because the in-game FoV is horizontal FoV and the webtool is asking for the vertical FoV. There are various converters to find this value, or you can look in one of the game files: Go to your game installation folder, then open "user/profiles/default/attributes.xml". So something like "C:\Program Files (x86)\Steam\steamapps\common\Hunt Showdown\user\profiles\default\attributes.xml". Search for "FieldOfView" in this file to find " <Attr name="FieldOfView" value="58.7155"/>" Whatever value you have is your vertical FoV and should be put into the webtool (the example above is for 90 horizontal FoV = 58.7155 vertical FoV).
   
6. If you run the game at your monitor's native resolution, then you don't need to change "Game Resolution & Scaling Mode".
   
7. If you haven't changed windows mouse settings or windows display scale settings then you don't need to change the "Pointer Speed" or "Display - Scale and Layout" sections.
   
8. Put your mouse DPI in the "Mouse CPI" section (CPI = DPI).
   
9. Input your monitor size (this is the diagonal length).
   
10. Input your monitor resolution.

***Before you read the various sensitivity values:*** The webtool's "Hipfire" and "Shoulder Aim" do not refer to what they sound like. Instead, they refer to your in-game settings for "Lowered state field of view" and "Shoulder aim field of view". The webtool's "Hipfire" is the "Default" state and the webtool's "Shoulder Aim" is the "Zoom" state. If you have both these settings set to default then use the webtool's "Hipfire" for both in-game "Default" and "Shoulder Aim" sensitivities. If you have the field of view settings both set to "Zoom", then use the webtool's "Shoulder Aim" value for both "Default" and "Shoulder Aim" sensitivities. And if they are different use the respective value.

If that sounds confusing here is an example where both "Lowered" and "Shoulder Aim" are set to "Default" state (not to "Zoom" state):

Note the "Visuomotor (gain)" column in the second table. They should all be identical in our case. You can write this number down (for me it's 4.55) so if you change something later (field of view/monitor/resolution/etc.) you can come back and use the visuomotor value to find your equivalent sensitivities.

If you were to do this you would set "Sensitivity Units" to "Visuomotor" instead of "Virtual" on the webtool. You would then fill in your visuomotor value along with the rest of the inputs and you can see your respective sensitivities again in the first table.