At the same time, the research firm expects total retail sales around the world to increase 6% to $22.05 trillion this year, and then maintain a similar growth rate until 2020 when total global retail sales are forecast to top $27.7 trillion.
But it is the projected growth of retail e-commerce over the next few years that stands out in the report, which expects digital sales to continue recording double-digit increases through to 2020.
While the pace of growth of retail e-commerce sales is expected to slow, eMarketer expects them to account for just over $4 trillion in 2020 and to make up 14.6% of total retail spending that year. Travel, event ticket and restaurant sales are excluded from the forecast.
Much of the growth and volume of retail e-commerce is projected to come from China, where sales are expected to reach $899.09bn this year, or almost half (47%) of all such sales worldwide.
The strength of e-commerce in China means that Asia-Pacific will remain the world's largest retail e-commerce market over the next four years.
The report expects sales in the region to top $1 trillion in 2016, after recording 31.5% growth this year, and then more than double to $2.725 trillion by 2020.
Meanwhile, North America is expected to maintain its position as the world's second largest e-commerce region and retail e-commerce sales there are forecast to grow 15.6% this year to $423.34bn.
"The region will see consistent double-digit growth through 2020, fuelled by increased spending from existing digital buyers, expansion into new categories, such as grocery, and growing m-commerce sales," the report said.
Data sourced from eMarketer; additional content by Warc staff