As Eagle’s chart included in media research analyst Rich Greenfield’s tweet above shows, India is just over 30 million Facebook users short of the US, but growing at closer to 40 million users a year, nearly eight times the rate of the US.

Eagle’s projections are calculated in spreadsheets using Facebook’s current revenue by region and extrapolating into the future, assuming current growth rates. (Eagle’s mobile surveys business reaches about two billion people in the developing world.) Facebook didn’t immediately respond to a request for comment.

There’s no guarantee that this will indeed play out as Eagle predicts. But, even if it doesn’t precisely, this latest prediction highlights the remarkable pace of Facebook’s growth in the developing world. It also likely points to potential challenges Facebook could face in raising its average revenue per user, particularly since so much of Facebook’s usage in India is on mobile phones.

Eagle predicts that revenue will follow as advertisers learn how to better market their products via mobile platforms. The company’s most immediate priority should probably be to get as many of India’s more than one billion people to use it before a competing social network gets to them. “Convincing people to switch over [to Facebook] is a lot harder than simply getting them to join,” says Eagle.

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