Eight states plus the District of Columbia have already increased their minimum wages this year, the most to have done so in a single year since 2006, and at least eight other states and municipalities could put minimum wage ballot measures before voters by November. But it is the scale of ambition that is catching the attention of economists, labor leaders and business owners.

“In past rounds of minimum wage increases, proposals sought chiefly to restore the value of the minimum wage lost to inflation over the decades,” said Paul Sonn, the general counsel and program director at the National Employment Law Project, a New York-based group that supports raising the minimum wage. The increases in places like Seattle, Mr. Sonn said, go beyond playing catch-up. “The $15 proposals make real gains,” he said.

Economists who study the minimum wage are not sure of the effect of having sharply different levels — in some places, it is twice that of others. Though records are a bit uncertain, people who track minimum wage law say the range of mandated minimums, lowest to highest, is the largest it has been since a national minimum was established by Congress in 1938.

“Nobody has studied a doubling of the minimum wage — that’s outside our experience,” said Dale Belman, a professor of labor and industrial relations at Michigan State University and co-author of a coming book about the minimum wage.

Individual workers and business owners in and around Seattle are unsure of the implications. Washington State already has the highest state minimum wage in the nation, $9.32, but more than 24 percent of Seattle residents earn hourly wages of $15 or less, according to the city, and approximately 13.6 percent of Seattle residents live below the federal poverty level.

Under the plan approved on Monday, the hourly wage will rise to $15 by 2017 for employers with more than 500 workers that do not provide health insurance, and by 2018 for those large employers who do. The minimum will be phased in through 2021 for smaller employers.

In its early years, the law allows employers to include tips as part of a workers’ compensation in reaching the minimum, but that provision is phased out over time.