US mobile phone and tablet commerce will top $293 billion by 2018 (tablet = $219B; smartphone = $74B) — a whopping 54% of total US eCommerce sales. By the end of this year, combined mobile and tablet sales will reach $114 billion, with the biggest purchase categories including media products, apparel, and consumer electronics, according to a new Forrester forecast.

This growth is driven by nearly 200 million smartphone subscribers and nearly 100 million regular tablet users. However, because of the larger screens and easier form factor of tablets, Forrester expects the percentage of tablet buyers to eclipse the total percentage of smartphone buyers by 2018.

By comparison, Forrester forecasts total US online retail sales to reach $414 billion by 2018 — 11% of all retail sales. Online retail sales will grow at a 9.5% compound annual growth rate over the next five years, with $294 billion expected in 2014 online retail sales.

But all this growth certainly does not mean that stores are dying, writes Vice President and Principal Analyst Sucharita Mulpuru in a new blog post. “While we expect $150 billion to be spent online between now and 2018, we expect $300 billion more to be spent offline in that same time. Add to that the money up for grabs that dying retailers like Sears, OfficeMax, RadioShack, and others will leave on the table, and the opportunity for physical retail is actually quite large.”

To learn more about this research, visit the eBusiness & Channel Strategy blog here.