Online shoppers in the United States will spend $68.4 billion this holiday season, up 15% from the $59.5 billion spent in 2011, according to a report released today by Forrester Research Inc. Holiday shoppers will spend an average of $419 online this year, up 12% from last year, says the report, “US Online Holiday Retail Forecast 2012” by Sucharita Mulpuru-Kodali, vice president and principal analyst at Forrester.

She attributes the projected increase in e-commerce spending in part to more consumers shopping online instead of going to stores. “Web shoppers consistently report they often prefer to shop via the web channel during the holidays to avoid crowds and parking challenges,” the report says.

The web also will get a boost this holiday season from mobile commerce, the report says. By the end of the year, 135 million U.S. adults will own smartphones and 60 million consumers will own table computers, Forrester estimates. For consumers who already have those mobile devices, at least 18% of smartphone owners and 24% of tablet owners have purchased through those devices. “The mobile and tablet shopping trend tends to be amplified during the holidays as consumers spend more time shopping online with remote devices at home, in stores, and on the go,” the report says.

The report also finds that:

• 56% of U.S. consumers say they are more “price conscious” than a year ago, and 57% say they find better deals and value online, which is up nine percentage points from last year.

• 57% of consumers shop more online with merchants that offer free shipping, and 27% of consumers have bought “additional unplanned items to meet free shipping thresholds.”