According to Genesis, Noah’s Ark is 300 cubits long.
Genesis 6:15 gives the Ark’s principal dimensions as 300 cubits in length, 50 cubits in width, and 30 cubits in height. A cubit was an ancient unit based broadly on the length of a forearm, so its exact modern equivalent is uncertain. Using common estimates, 300 cubits is often rendered as roughly 135 to 150 metres, or about 450 to 500 feet.
The number 300 is sometimes confused with the Ark’s other measurements. Its width is 50 cubits and its height is 30 cubits; Genesis also describes three decks. The biblical text presents these measurements as instructions given before construction, rather than as dimensions recovered from an archaeological vessel.
Modern reconstructions vary because ancient cubits were not perfectly standardized. The biblical flood account also differs in some details from later Jewish, Christian, and Islamic traditions, but the 300-cubit length is the standard measurement in Genesis.