The biblical unit measuring Noah’s Ark as 300 units long in Genesis is the cubit. Genesis 6:15 gives the Ark’s dimensions as 300 cubits long, 50 cubits wide, and 30 cubits high.
A cubit generally referred to a length based on the forearm, commonly from the elbow to the fingertips. Its exact historical size varied by culture and period, so converting the Ark’s dimensions into modern units requires an estimate. Depending on the cubit used, the length is often calculated at roughly 135 to 150 metres.
The proportions are approximately six to one for length versus width and ten to one for length versus height. Those ratios have attracted attention from naval architects because they describe a broad, stable barge-like form. Genesis, however, presents the measurements as narrative instructions rather than a modern naval engineering specification.