You most likely know that Google is now using mobile-friendliness as a significant ranking factor. Websites that are not properly optimized for mobile devices will achieve lower rankings in mobile search results; and this is no small matter, given that mobile internet usage has now overtaken desktop usage.

If you’re still unsure to whether or not your site is mobile-friendly, here are 3 online tests you can use to determine the mobile-friendliness of your site.
 

1. Google’s Mobile-Friendly Test

Perhaps the simplest and most accurate tool out there, I recommend starting here.
Keep in mind that this tool checks via page, not domain; so just because one page “passes”, doesn’t mean every page on your site will.

2. PageSpeed Insights

The speed at which a page loads is a critical ranking factor. In fact, page speed may be an even more significant ranking factor than mobile-friendliness. 

To see how your page fares in terms of speed, usw Google’s PageSpeed Insights tool. It works much the same as the Mobile-Friendly Test, however it provides more detailed instructions as to how to speed up your page. This tool provides two separate scores out of 100: one for speed and one for user-experience. This score is available for both the mobile and desktop versions of your page.

3. mobiReady

mobiReady will appeal to those who are more visually-oriented. It renders how your page displays on various devices.

It also provides a mobiReady score between 1 and 5, as well as a detailed listing of CSS elements and whether each is a pass.
You will also see a benchmark of your site against the top 1000 sites on Alexa.

For more information about this and other tools on the market, you can visit  Jayson DeMers" article in Forbs magazine: