The official online spending numbers are in for 2012. U.S. e-commerce sales totaled $225.5 billion last year, up 15.8% from $194.7 billion in 2011, according to an estimate released today by the U.S. Commerce Department.

The estimate, not adjusted for seasonality, illustrates that online sales are continuing to account for a larger part of total retail sales in the United States. 5.2% of total retail spending took place online during 2012, up from 4.7% in 2011, according to the U.S. Commerce Department.

On a non-adjusted basis, when excluding sales in categories not commonly bought online—automobiles, fuel and foodservice sales—Internet Retailer calculates that e-commerce accounted for 7.6% of total retail sales during the year, up from 6.8% a year earlier.

On a non-adjusted basis, total retail sales, which include e-commerce sales, totaled $4.4 trillion in 2012, up 4.8% compared with $4.2 trillion in 2011, according to the Commerce Department.

The e-retail sales totals released by the Commerce Department today align closely with forecasts made in early 2012. Forrester Research Inc. had predicted $226 billion in 2012 online sales, while eMarketer predicted sales of $224.2 billion.

E-commerce sales for the fourth quarter totaled $71.6 billion on a non-adjusted basis, up 36.3% from the third quarter of 2012 and up 15.8% year over year. Total retail sales increased 4.0% in Q4 to reach $1.2 trillion.

On a non-adjusted basis, when excluding sales in categories not commonly bought online—automobiles, fuel and foodservice sales—Internet Retailer calculates that e-commerce accounted for 8.8% of total retail sales during the fourth quarter compared with 7.8% a year earlier.

The Commerce Department figures are higher than those released earlier this month by comScore Inc. The web measurement firm says online shoppers in the United States spent $186.2 billion in 2012, up 15% from 2011. The web measurement firm says that e-retail sales in the fourth quarter of 2012—which covers the holiday shopping period—increased 14% year over year to reach approximately $56.78 billion. ComScore draws on online purchase data from its panel of about 1 million U.S. online shoppers. Commerce Department estimates are based on a quarterly survey of more than 11,000 U.S. merchants.

Other estimates released last month by Shop.org, the National Retail Federation’s online digital division, says that for 2012, total retail sales, excluding sales of vehicles and parts, increased 4.9% and non-store retail sales increased 11.6%. Non-store sales largely come from online retailers but also merchants that sell through catalogs and TV infomercials. It also says non-store sales grew 11.1% for the last two months of 2012, compared with the same months a year earlier. Shop.org and the NRF didn’t release dollar figures.

For the year, the trade group predicts online sales will increase between 9.0% and 12.0% in 2013 over 2012, again outpacing total retail sales, which it estimates will increase 3.4%.

Another report from IBM released this week says online shoppers spent nearly 15% more in the fourth quarter compared with a year earlier.  IBM did not provide a dollar figure to accompany its estimate and it did not provide full-year growth estimates. IBM culls its estimates by examining data from more than 500 of its retailer clients.

ComScore today added further detail on consumer online spending trends. For example, 14% to 15% of U.S. total spending on apparel in Q4 2012 was online, it says. Moreover, online spending via portable devices like smartphones and tablets was up 46% year over year in Q4.

Sales via tablets increased 49% year over year in Q4, comScore says, adding that tablet sales will be one of the top e-commerce trends to watch in 2013 along with social networking sites—led by Pinterest, which hit an all-time high of 29 million unique visitors in December 2012, up by 3 million from November 2012, comScore says.

Amazon continues to dominate as the Internet retailer with the largest number of average monthly unique visitors in Q4, 115 million, up 3% year over year, comScore says. Macy’s also increased site traffic notably in the fourth quarter, by 11% year over year, to 18.4 million unique visitors, it says. And many flash-sales sites showed double-digit year-over-year traffic growth, too. Fab.com led the way among them, with a 329% year-over-year increase in average monthly visits in Q4, translating to 2.917 million unique visitors.

For 2013, comScore forecasts e-commerce spending will grow in the mid- to- high-teens, percentage wise.

Amazon is No. 1 in the Internet Retailer Top 500 Guide. Macy’s is No.14, Fab.com is No. 449.

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