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The Big Mac index, created by the Economist magazine in 1986, is a PAUL J. RICHARDS / AFP - Getty Images file

Fast-food workers went on strike recently in hopes of persuading politicians to raise the minimum wage. But how does the U.S. minimum wage compare internationally?

Strategists at ConvergEx Group have compared minimum wages around the world using an unlikely tool: the burger.

"We wanted to see where the U.S. minimum wage ranked on an international scale, so we took a fairly well-known indicator, the Big Mac index, and compared burger prices to minimum wages in different countries," the researchers wrote in a note.

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"It's near impossible to gauge apple-to-apples, of course, so we took a different route for comparison: How many hours does it take to earn a Big Mac at minimum wage?"

(Read more: Will fast-food protests spur higher minimum wage?)

The Economist created the Big Mac index in 1986 as "a lighthearted guide to whether currencies are at their 'correct' level," according to the British magazine's website.

Last month, for example, the average price of a Big Mac was $4.56 in the U.S. and $2.61 in China at market exchange rates.

At $7.25 an hour, the U.S. has the seventh-highest minimum wage on an absolute basis; Australia has the highest, at $16.88. The lowest: Sierra Leone's 3 cents an hour.

Here's how many hours it takes to earn enough for a Big Mac around the world:

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"If we compare apples-to-apples how many hours it takes to earn a Big Mac at minimum wage, the U.S. again comes right in the middle at number 8," ConvergEx found.

It takes 34 minutes working at the U.S. minimum wage to earn enough to buy a Big Mac, 22 minutes in France and New Zealand, and just 18 minutes in Australia. In India, it takes 6 hours.

A worker in Sierra Leone would have to put in 136 hours, or more than three weeks at 40 hours a week.

—By CNBC's Justin Menza. Follow him on Twitter @JustinMenza.