The Internet accounts for 4.7% of the U.S. economy and is projected to grow 6.5% a year through 2016, according to a new report.

The Boston Consulting Group took a look at the top 20 global economies — also known as the "G-20" — and found lots of reason for optimism. On average, the Internet economy is expected to grow 10.8% for the G-20. However, the expansion in developed countries like the U.S. will be on the low end, around 8%, while developing countries like Argentina and India will expand at rates of 24% and 23%, respectively, according to the report. (Registration required.)

Meanwhile, in the U.S., the Internet accounted for $684 billion in economic activity in 2010 vs. $625 billion for the federal government, whose share of the U.S. economy is 4.3%. In the U.K., the Internet's share of the economy is 8.3%, the highest of any of the countries surveyed. Next on the list is South Korea with 7.3%.

By 2016, the Internet will account for 5.4% of the U.S. economy. It will account for 12.4% in the U.K. and 8% in South Korea, according to the study.

If anything, the report understates the Internet's influence on such economies. The percentages, for instance, would be higher if you accounted for the phenomenon of "research online, buy offline" (ROPO), which applies to 7.8% of consumer spending in the G20, or $900 per connected consumer.

Although cars are a typical ROPO purchase in the U.S., many consumers in China research and plan for their grocery shopping online. In India, tech products are frequently ROPO. That effect is being amplified by the growth of the mobile web, which lets consumers research such purchase decisions while they're in stores.

Such technology is a major factor in the growth of the Internet economy, but so is demographics: The younger you are, the more likely you are comfortable using the Internet.

Image courtesy of iStockphoto, PashaIgnatov