Did you know the length of a river can be very hard to calculate. The length measurements of many rivers are only approximations. In particular, there has long been disagreement as to whether the Nile or the Amazon is the world's longest river. The Nile has traditionally been considered longer, but in recent years some Brazilian and Peruvian studies have suggested that the Amazon is longer. For the purpose of determining maximum length a river's "true source" is considered to be the source of whichever tributary is farthest from the mouth.
World Map - The longest rivers on the planet
Check the World Map showing location of top ten longest rivers by length in Kilometers. While Nile River is the longest river on earth with length of 6,695 km. and number two is Amazon River with 6,516 km.