Site statistics: What is the proportion of mobile device screens?

Question

Analytics

Tell me where you can see the most reliable summary / statistics / analytics of visits to all sites by users from various devices. Interested in the growth rate of the percentage of mobile screen width relative to desktops over the past few years. Preferably in Russia and around the world separately.
And more specifically, what is the increase in the percentage of purchases of goods online from mobile devices from websites and applications?
To determine how urgently it is necessary to make an adaptive mobile version in online stores, or anyway, only 10-15% of users will make a purchase or order paid services with payment online from a mobile device, at least for 2015.

Answer 1

Permission stats from w3schools.com
Here's more about cross-device purchases

Answer 2

1) an adaptive mobile version has been available everywhere since April 2015 and February 2016 (in the Russian Federation)
2) globally, the number of mobile traffic can be estimated from the same similarweb, on average, about 30% for sites (in messengers, of course, higher), which, of course , above 15-20% in 2014
3) specifically for devices - counters, you can search for small ones, from large ones:
gs.statcounter.com
https://www.liveinternet.ru/stat/ru/browsers.html - only here xs how divided into mobile

Answer 3

It turns out that views from mobile devices are actively growing at 15% per year and now occupy about 50% of all views, however, the percentage of purchases from mobile phones and tablets is no more than 25% together, and individually no more than 15%.
From which we can conclude that it is necessary to deal with the mobile version of the site immediately after the development of the necessary functionality and its output in the public part in the desktop version. And after the ready-made adaptive mobile version, proceed to the development of usability improvements for the current functionality.
If there is a good TOR for the project and time with finances allows, then the time has already come when both the desktop version and the adaptive mobile display (single-column) of less than 1000px of screen width should be developed together, so as not to lose the mobile share of users.