I think you can find the answer at this website: https://dvdfab.org/
There are some Photoshop related articles in there.
There is a software that can solve your problem:https://dvdfab.org/ai-suite.htm

I think it would be useful to view the letter spacing in different units like px, but for the design work it is actually really practical to have it in a unit relative to the font size. Otherwise you would have to adjust the letter spacing everytime you increase or decrease font size, just that the text keeps looking the same relative to its new size.

I made a codepen to help you everyone with this till XD launches their own solution
You can find it here: https://codepen.io/raunaqpatel/full/bGpwBvo

Is this being looked at? am finding it a headache to work out the correct numbers so that the development team can be accurate:

I have a Header text at 61px with AV set to 16.4. In code this equates to -1px in the code which is what I want.

Then I created a larger header size at 80px but 16.4 AV = -1.31px in code;

I now have to spend time with trial and error to get my larger text size to -1px

To make XD more successful it needs to be a tool that can be used across all team disciplines. and be design for digital

I didn't know that I needed a calculator to use this programm...If adobe wants to make a better user experience for their users please change this to pixels, no one understands this system! For type / font systems styleguides this is a horrible user experience! Lately they just released "marketing features" for new users, instead of focusing in the users that use this professionaly...

WTF is that?

I just found out now why the devs I'm working with hated me and was having so bad results from my designs!
Go explain to a dev that you choose "-0.84px" as a letter spacing better than a more round number.

I found this reply from XD team:
- "We’re working in milli-ems, which is 1/1000th of the point size of the font.”

Really? Can we have a least a reason for that? I mean, why not "kilo-pourcentage"?

Give us at lease the choice. Web devs or app devs are not same devs.
Please Adobe!
em / px / pt / dp.. as you do on other softs. Please keep it more consistent.
The worst thing is, you make the conversion to px/pt ton the shared link!
Give us the same within the application!

And sorry for the grumpy tone of my message, but now I have to redo +25 screens because of this.
And make scientific calculation for something as essential as letter spacing..

Thank you in advance!

Indeed, really needed when sharing designs with front end developers – px/rem is a more saying value for the most developers than AV.

The having av is a crazy notion as there is no correlation in px

Me and the designer I work with are very impressed with this software, but one of the issues I keep coming across is the units that kerming is measured in. Most of the other values of colours, font sizes, padding etc is transferrable in to CSS but not the kerning values. Could a unit size be added whether that be something like px / rem.

Definitely. I have no idea what the units are right now for letter-spacing. I had to make it 50 units, just to get it look like 0.5px