This Cyber Monday was the busiest online shopping day in history with online sales of $1.47 billion, a 21 percent increase from last year, according to the NPD Group.

The increase in sales comes not from a boost in the number of people going online, but an increase in the number of shoppers who were converted to buyers.

This year, 17 percent of consumers reported shopping online on Cyber Monday compared to 16 percent last year, but of those shoppers, 58 percent made a purchase compared to 47 percent in 2011, spending roughly 12 percent more than last year on average.

And the Cyber Monday effect isn’t exclusive to America either. Cyber Monday online sales are spreading to other parts of the world as U.S.-based global retailers expand their promotional strategies globally. This year in Europe, Cyber Monday sales were up 8 percent a according to the Adobe Digital Index.

The growing trend toward e-commerce is reflected not only in sales figures but also in consumer behavior, where the number of shoppers using mobile devices and engaging in “showrooming” is growing exponentially.

Adobe reports that $1 out of $4 spent online this year are coming from a mobile device, and shoppers are also using their mobile devices to “showroom,” the practice of visiting retail stores to try products, but then checking a mobile device for the best price online.

New research from Aprimo, conducted by Harris Interactive, found that one in five shoppers in the U.S. are showrooming. When NPD asked consumers their reasons for shopping on Cyber Monday, the No. 1 answer (51 percent) was “I wanted to compare prices and deals,” up 27 percent from last year.

And the practice isn’t just for big-ticket items.

While consumer electronics are the most popular items price-checked in store (39 percent), groceries (37 percent) and apparel/footwear (33 percent) follow closely behind.

“This year, 68 percent of shoppers stated they have completed their shopping, compared to last year’s 69 percent, which tells us there is still more to come. Retailers have their work cut out for them,” said Marshal Cohen, chief industry analyst, The NPD Group. “Even with the great start out of the gate, this race still has a long way to go.  Consumers may have just spent themselves out until the next paycheck, so look for retailers to use more sales and specials to entice the consumer to keep shopping throughout the remainder of the holiday season.”