In part, the GDP is the government's way of computing the unemployment rate of the United States. To compute the rate of unemployment, you must first calculate the actual GDP and subtract it from the potential GDP.

Actual GDP, also called productivity, is simply the amount of output per man hour worked in the economy during a particular period.

Potential GDP is the Output per man hour times total man hours available to be worked during a particular period.

As long as Actual GDP is less than Potential GDP, unemployment occurs. However, full employment does not mean that employment is at a full 100%.

see: full employment