As a proliferation of Web-enabled smartphones is expected to help a total of 3 billion people access the Internet by 2016, online retail, banking, advertising, IT services and demand for Internet-related goods will thrive, BCG said on Monday.

The G20's Internet economy will nearly double between 2010 and 2016, creating an extra 32 million jobs, according to the BCG report.

"If it were a national economy, it would rank in the world's top five, behind only the U.S., China, India, and Japan, and ahead of Germany," said David Dean, BCG senior partner and a co-author of the report.

In developed markets, the Internet economy will grow at about 8 percent annually, while in developing markets it will grow more than twice as fast, according to BCG.

Overall G20 GDP grew 2.8 percent last year, according to the Organisation for Economic Cooperation and Development, and is expected to slow this year.

BCG said the Internet economy in Britain accounted for 8.3 percent of gross domestic product in 2010, the highest percentage of any G20 nation, thanks to widespread access, good infrastructure and high credit-card usage.

In South Korea, the Internet contributed 7.3 percent of GDP, in China it was 5.5 percent and in the United States 4.7 percent, BCG said.

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