How many cubits long does Genesis say Noah's Ark was?

Genesis says Noah's Ark was 300 cubits long. Genesis 6:15 gives its principal dimensions as 300 cubits in length, 50 cubits in width, and 30 cubits in height.

A cubit was an ancient unit based approximately on the length of a forearm, but its exact value varied by culture and period. Using a common estimate of about 45 centimetres, 300 cubits would be roughly 135 metres, although the conversion is not certain.

The text describes a boxlike vessel with three decks, rooms, and a window, rather than a ship with a detailed nautical design. Modern replicas and comparisons with ancient boatbuilding therefore depend on assumptions about the cubit, the shape of the hull, and the meaning of some Hebrew terms. The number 300 itself is the direct biblical measurement.