  This paper aims to compute the unemployment rate $u^*$ that is consistent
with full employment in the United States. First, it argues that the most
appropriate economic translation of the legal notion of full employment is
social efficiency. Here efficiency requires to minimize the nonproductive use
of labor -- both unemployment and recruiting. The nonproductive use of labor is
measured by the number of jobseekers and vacancies, $u + v$. Through the
Beveridge curve, the numbers of vacancies and jobseekers are inversely related,
$uv = \text{constant}$. With such symmetry the labor market is efficient when
there are as many jobseekers as vacancies ($u = v$), inefficiently tight when
there are more vacancies than jobseekers ($v > u$), and inefficiently slack
when there are more jobseekers than vacancies ($u > v$). Accordingly, the
full-employment rate of unemployment (FERU) is the geometric average of the
unemployment and vacancy rates: $u^* = \sqrt{uv}$. Between 1930 and 2023, the
FERU averages $4.1\%$ and is quite stable -- it always remains between $2.5\%$
and $6.6\%$.
