Nominal versus Actual: A History of the 2x4

> Lumber size standards came into being almost a century ago to meet the need for a common understanding between the mill and markets that were separated by increasing distances of rail or water transportation. Early concepts called for rough lumber to be of full nominal size, often in the dry condition. After World War I, the increasing demand for construction lumber led to the first national size standard in 1924. This was revised in 1926, 1928, 1939, and 1953, while still another revision is proposed for adoption in 1964 ... Economic pressures among the regional areas of lumber production have resulted in a decrease of standard lumber sizes over the period covered by this history.

In European countries wood is more rare and they build cement houses. More expensive but more durable.