Using data from the International Air Transportation Agency (IATA) as well as individual travellers, the site's creators crunched the numbers and determined a passports' Visa Free Score, or the number of countries that allow its holder to enter without a visa or obtain one upon arriving. The higher the Visa Free Score, the higher the "Passport Power Rank."
Unsurprisingly, the US and UK are the most widely accepted in the world with 147 nations opening their doors to travellers visa-free. Tied for second place are France, Germany, and South Korea, with 145 countries. Nations in conflict like the Palestinian Territories and South Sudan bring up the rear.
The site also features a map where users can click on a country to see the corresponding passport. If power rankings aren't your thing, you can sort the passports by colour.
As part of an ongoing, interactive project, users are also invited to contribute pictures of their passports to make a more complete database.
Check out the range of passport colours from all over the world below.