Planet Instagram: The social media app has 3 billion users. But who counts?

Instagram has always been pretty precocious. Now, just ahead of its 15th birthday, we have a new measure of its global fame — and it is on a level far beyond the dreams of regular teenagers.

Meta CEO Mark Zuckerberg announced Wednesday that the once-humble photo-sharing app, which he had the foresight to buy for a mere $1 billion in 2012, now has more than 3 billion active users. That's an extraordinary achievement, and not just because Instagram had barely cracked 30 million monthly active users at sale time.

Three billion is nearly 37 percent of the population of Earth. If it were a country, Instagram would be larger than India (which has the largest Insta audience), China, the U.S. and the E.U. combined. The Roman Empire, the British Empire, the American whatever-this-is — they can only drea...