WASHINGTON – U.S. workers were more productive from April through June than previously estimated while labor costs were unchanged.

Productivity grew at an annual rate of 2.3 percent in the April-June quarter, up from an initial estimate of 0.9 percent growth, the Labor Department said Thursday. Unit labor costs were flat in the second quarter, less than the 1.4 percent rise the government had initially estimated.

The combination of stronger productivity and less of an increase in wages should provide assurances to the Federal Reserve that inflation is not a threat.

The revised productivity number reflected the fact that economic output had been revised higher for the second quarter to a growth rate of 2.5 percent. Productivity is the amount of output per hour work.

The 2.5 percent economic growth rate was much stronger than the 1.7 percent annual rate estimated a month earlier for the gross domestic product, the economy’s total output of goods and services.

Still, even with the increase, productivity growth has been weaker than during the recession and early stages of the recovery. It rose just 1.5 percent in 2012 and 0.5 percent in 2011. In 2010 and 2011, productivity increased at annual rates above 3 percent. That reflected the fact that millions of Americans were laid off as companies struggled to cope with a deep downturn. While output was down as well, the number of workers fell more, thus productivity increased.

In records dating back to 1947, productivity has been growing by about 2 percent per year.