What is the best screen size to design for in 2015? This was most definitely one of the first questions I had as a young(ish) web designer with an interest in web accessibility 15 years ago or so.The most satisfying answer I ever found was: Design for YOUR audience first, masses second.That’s basically how I got by.

But – Google may have just decided for everybody on this long discussed question.

Google dictates the ebb and flow of online commerce and they’ve just dictated you need to design for a good experience across multiple devices IF you want to rank well in Google.

Starting April 21 (2015), we will be expanding our use of mobile-friendliness as a ranking signal. This change will affect mobile searches in all languages worldwide and will have a significant impact in our search results. Consequently, users will find it easier to get relevant, high quality search results that are optimized for their devices. GOOGLE

So from April 21 2015, all around the world, how mobile friendly a site is WILL affect ranking performance across a variety of devices.

If you make websites for small businesses – you’ll know they want a website that will perform well in Google organic listings. That performance is now based around good website UX, as Google quantifies it, at least for mobile users. At the moment – that essentially now means responsive website design.

Source: What Is The Best Screen Size to Design Websites in 2015