Genesis uses cubits for the ark’s length, width, and height.
Genesis 6:15 gives the ark’s dimensions as 300 cubits long, 50 cubits wide, and 30 cubits high. A cubit was an ancient unit traditionally associated with the length of a forearm, but its exact historical length varied by culture and period.
Because the cubit was not a single universal standard, converting the ark’s measurements into metres or feet involves interpretation. A commonly used estimate places the ark near 150 metres long, 25 metres wide, and 15 metres high, but the precise modern conversion cannot be established from Genesis alone.
“Cubits” is therefore the canonical answer to the unit question. The numbers describe the biblical narrative and should not be mistaken for measurements verified by an existing vessel.