How to determine screen resolution/size?

Question

css

So, the essence is this: the Client came with the Xiaomi Mi6 device and shows the jambs in the adaptive version. Judging by the display, an adaptive version for a width of 360 pixels, but the screen resolution of this model is Full HD (1920x1080). And how do you determine which version of adaptives show modern devices?
PS The diagonal of this smartphone is 5.15 inches, can it be repelled from it?

Answer 1

Read - https://habrahabr.ru/post/237931/
a very useful article, I think it will answer your question.

Answer 2

Open from your smartphone https://www.esolutions.se/en-GB/test

Answer 3

It's all about pixel density. the same iPhone 5 - 1136 x 640 pixels, 326 pixels per inch - this means that in the same chrome dev-tools it will be indicated as 320 pixels, but in fact, on the iPhone itself it will be 640 pixels due to the double, in relation to ordinary monitor, pixel density ...
unfortunately you have to read the article indicated by Nikolai))

Answer 4

Is the Javascript option not suitable?
screen.width