According to Genesis, Noah’s Ark was 300 cubits long.
Genesis 6:15 gives the Ark’s dimensions as 300 cubits in length, 50 cubits in width, and 30 cubits in height. The cubit was an ancient unit generally based on the length of a forearm, so its exact modern equivalent is uncertain. Estimates commonly place the Ark’s length somewhere around 135 to 150 metres, depending on which cubit standard is used.
The dimensions produce a long, boxlike vessel rather than the shape of a conventional sailing ship. Genesis also mentions a roof, rooms, and an opening, but it does not provide a complete engineering plan or identify a precise cubit length.
The number 300 is sometimes confused with the Ark’s width or height. Those measurements are 50 and 30 cubits respectively. The famous length-to-width-to-height ratio is therefore 300:50:30, or 6:1:0.6.