In Genesis, Noah’s Ark is stated to be 300 cubits long.
Genesis 6:15 gives three dimensions for the vessel: 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, but its exact historical measurement varied. For that reason, translations usually preserve the word “cubit” rather than converting the figure into one universally agreed modern length.
Using a common estimate of about 18 inches per cubit, 300 cubits would be roughly 450 feet, or 137 metres. That conversion is approximate, while the biblical figure itself is explicit. The text presents the dimensions as instructions given to Noah before the flood.
Readers sometimes remember 300 cubits as the ark’s total size rather than its length. The other two measurements are 50 cubits wide and 30 cubits high.