One of the hallmarks of a world traveler is a well-worn passport, and it is estimated that more than 160 million passports are currently in circulation. But not every passport is created equal.

The strength of the world's passports is measured by the International Air Transport Association in its annual Henley Passport Index, which measures "visa-free access to 227 destinations across the world," CNBC said. Henley also factors in "mobility data" based on national GDPs and the percentage of global wealth each passport could provide access to. Data shows that international travel is getting easier — Henley estimates that the average number of global destinations a passport holder can access is 111.

These are 10 of the world's most powerful passports, according to Henley's Octob

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