Can you guess the 9 most popular websites? To get that data, I turned to Alexa's Global 500, which ranks sites based on traffic. While their rankings aren’t perfect, the “Alexa number” is a common metric when comparing things online. Mentalfloss.com is #8,179 (#2,166 in the U.S.), but we won't make you count that high. You can just enter the site's name (Google), not the URL (www.google.com).