How Large are the U.S. Economy Gains from Trade?

From a working paper by Arnaud Costinot and Andrés Rodríguez-Clare: 

Abstract: 

About 8 cents out of every dollar spent in the United States is spent on imports. What if, because of a wall or some other extreme policy intervention, imports were to remain on the other side of the US border? How much would US consumers be willing to pay to prevent this hypothetical policy change from taking place? The answer to this question represents the welfare cost from autarky or, equivalently, the welfare gains from trade. In this article, we discuss how to evaluate these gains using the demand for foreign factor services. The estimates of gains from trade for the US economy that we review range from 2 to 8 percent of GDP. 

A less technical overview is presented in the NBER Digest from April 2018