The Book of Genesis says Noah's Ark was 300 cubits long. The same passage gives its width as 50 cubits and its height as 30 cubits, describing a very large rectangular vessel built from gopher wood and coated with pitch.
A cubit was an ancient unit based roughly on the length of a forearm, but its exact value varied. Depending on the measurement used, 300 cubits is commonly estimated at about 135 metres, or 450 feet. The biblical text gives proportions rather than a modern metric measurement.
The Ark's dimensions are often compared with later ships, but Genesis does not provide a complete naval blueprint. It mentions decks, rooms, a door, and a window, while leaving many construction details unspecified. The dimensions belong to the biblical narrative and should not be confused with the measurements of any modern replica.