In Genesis’s description of Noah’s Ark, the vessel is 300 cubits long.
Genesis 6:15 gives the Ark’s dimensions as 300 cubits long, 50 cubits wide, and 30 cubits high. A cubit was an ancient length based broadly on the distance from an elbow to a fingertip, so its exact modern equivalent is uncertain. Using common estimates, 300 cubits is often rendered as about 135 metres or 450 feet.
These measurements belong to the biblical text, not to a surviving archaeological vessel. Modern replicas choose a particular cubit length and therefore vary slightly. The Ark’s stated proportions—six times its width and ten times its height—have also attracted discussion about whether the design resembles a stable barge.