The FIETS Index was created by the Dutch cycling magazine "FIETS" as a way to compare the difficulty between climbs. The formula takes into account the length, altitude gained, and final altitude. The higher the number, the tougher the climb. Measuring the peak elevation allows the index to weigh the increased difficulty of climbing as atmospheric oxygen decreases.

PJAMM Cycling has an outstanding website with a database of over 4,000 climbs. Using the FIETS Ranking allows you to compare your favorite local climbs with climbs all over the world.