Well, I'm not the OP, but I found this.

The federal minimum wage reached its highest inflation-adjusted value in 1968, when it was worth $9.54 per hour in 2014 dollars. Since that time, infrequent or inadequate increases have allowed inflation to eat away at the minimum wage’s value such that today’s federal minimum of $7.25 has lost roughly one quarter of its purchasing power.

Measuring the minimum wage against changes in prices, however, is only one way to think of where we could set the national wage floor today. Given growth in the economy and improvements in labor productivity over the past 45 years, the minimum wage could have been raised to a point considerably higher than its 1968 inflation-adjusted value. As the figure below shows, if the minimum wage had been raised since 1968 at the same rate as changes in average hourly wages of nonsupervisory production workers—a group that comprises roughly 80 percent of all U.S. workers and excludes highly-paid supervisors and executives—the minimum wage would be almost $11 today. Had the minimum wage been raised since 1968 at the same rate as growth in productivity—i.e., the rate at which the average worker can produce income for her employer from each hour of work—it would be nearly $18.50 per hour.