My end goal is to display an image of the same exact size on every screen (yes, I really do need this for something). 

I started reading about how to get the user's screen size [here](https://stackoverflow.com/questions/21680629/getting-the-physical-screen-dimensions-dpi-pixel-density-in-chrome-on-androi) - and the answer seems to be that it's impossible (without calling an API which attempts to guess the actual device based on some params).

I then remembered that css has physical dimension units for sizing elements and decided to test on my screen. I set dimensions like so:

```
<div style = "background-color:black; height: 5in; width: 3in;"></div>

```

and then put a physical 3"x 5" (7.6cm x 12.7cm) flashcard against the screen.

It was significantly off in size.

Fun note - setting size in mm was ridiculously off - I expected to get the same results as with inches. 

With that said, is there a way to do what I need?