Swipe length in physical approximation

I am working on a game where I am using touch input (new Input system, Unity 6)

I have written an inputManager script to handle touch input and that works fine.

Because of the many types of touch input devices and different screen sizes and pixel density, I want to try to make a solution that work for all devices.
In essences I need the swipe length in cm(or some metric that for how long distance the swipe is in the physical world).
The idea is that I would then have one type of float that would be easier to balance across devices and also to use in terms of determining swipe speed.

What I have tried.
I have the distance in pixels

swipeDistance = startPos - playercontrols.Touch.TouchPosition.ReadValue<Vector2>();

But this value changes depending on screen resolution. I have tried to normalize this. I have tried to divide it with Screen.width and also Screen.dpi. but no matter what it yields different results on same length swipes on different screensizes.

Is there some way to measure the physical distance of a swipe? What is the standard practice for this?

Thanks