The web will account for or influence 59% of U.S. retail sales by 2018, up from 52% this year, according to Forrester Research Inc.

Its new report, entitled “U.S. Cross-Channel Retail Sales Forecast: 2014 to 2018,” also anticipates sales consumers begin via a digital medium but complete offline will account for $1.774 trillion in retail spending in 2018, up from $1.386 trillion in 2014.

“Consumers are ‘preshopping’ across more categories on digital devices, including phones and tablets, while the availability of more information at shoppers’ fingertips even when they are on the go is a significant driver of the growth in cross-channel shopping,” writes report author and Forrester e-retail analyst Sucharita Mulpuru. 

The reports notes that such product categories as food and furniture lend themselves to those web-influenced sales more often than for such categories as event or movie tickets, which don’t require as much online research before buying.

Other factors driving web-influenced sales include:

• Smartphone ownership, with 68% of U.S. online adults now  using their phones to access the web inside stores, according to Forrester. It adds that only 24% of U.S. online adults today use the devices to place orders for physical goods.

• Retailers’ “omnichannel efforts,” which include store associates using mobile devices to check inventory.

• The relatively small size of e-commerce in relation to the U.S. retail economy; between 2014 and 2018, Forrester says, 75% of U.S. retail sales growth will  come from offline sales, including those influenced by the web.

Forrester expects U.S. e-commerce sales—that is, purchases made online—to reach $414 billion in 2018, up from $294 billion this year. Earlier this year, the U.S. Commerce Department pegged U.S. e-commerce sales in 2013 at $262.51 billion, up 16.9% from the previous year, according to the department’s seasonally adjusted figures.