Genesis gives Noah’s Ark a length of 300 cubits.
Genesis 6:15 lists the Ark’s dimensions as 300 cubits long, 50 cubits wide, and 30 cubits high. A cubit was an ancient unit commonly related to the length of a forearm, but its exact value varied by culture and period. For that reason, converting the Ark into modern metres or feet is necessarily approximate.
Using a cubit of roughly 45 centimetres would make 300 cubits about 135 metres, though other estimates are possible. The text’s clear point is the ratio: the Ark was much longer than it was wide or high. The figure should not be confused with its width of 50 cubits or height of 30 cubits.