How to calculate the size of the picture (resolution) for the phone?

Question

Mobile development

Hello. Got a question. I will try to explain the essence of the issue with an example. There is a resolution of 1920x1080 on PC and Phone. The resolution is the same, but the actual display size is different.
In my head, you can draw a picture smaller and it will look acceptable on the phone.
But on the PC this trick will not work.
Precisely because I am writing an application on the phone. Where there are large background pictures, I wondered in what resolution to draw. Or how to count what would + - look normal. All pictures to draw in 2k is quite a difficult task. In addition, there are different screens. And here on a small device you can no longer make the window locked to a certain scale.
I will accept any advice, articles, notes and so on. On this topic.

Answer 1

Do not forget that the height of the phone is an order of magnitude greater than the width. Usually resolution is described in width/height format (as for example on a computer monitor). In the case of the phone, it goes the other way around.
In fact, for the phone you need to make a picture not 1920x1080, but 1080x1920. Try it.