Okun's coefficient and the empirical relationship
Okun's law takes the form Y~=−β(u−u∗), where β>0 is the Okun coefficient. The negative sign reflects the inverse relationship: unemployment above the natural rate is associated with output below potential. Empirical estimates for the United States typically place β in the range of 2 to 3, meaning each percentage point of excess unemployment corresponds to a 2-3% output gap. The relationship can equivalently be written in changes: ΔY/Y≈3%−2Δu, where 3% is a rough estimate of normal output growth. If the unemployment rate rises by one point, output growth falls about two points below trend.
The coefficient β exceeds one because of several amplifying channels. When firms face lower demand, they reduce not just headcount but also hours per worker, effort intensity, and overtime. Productivity tends to fall in recessions (labor hoarding means more workers per unit of output), which amplifies the output loss per unit of unemployment increase. Conversely, in booms, firms increase hours and effort before hiring, so output rises faster than unemployment falls. The Okun coefficient captures all of these margins and is best interpreted as a summary statistic of the labor market's response to demand fluctuations, not a structural parameter.
Y~=−β(u−u∗) Okun's law: the output gap is proportional to the unemployment gap, with coefficient β≈2-3 for the U.S.
YΔY≈g∗−βΔu Growth-rate form: actual GDP growth equals trend growth minus the Okun coefficient times the change in unemployment.
β≈2(U.S. postwar average) A one-percentage-point rise in unemployment is associated with roughly a 2% decline in output relative to potential.