In Genesis, chapter 6 first gives the dimensions of Noah’s Ark.
Genesis 6:14–16 introduces the Ark’s construction and specifies its materials, compartments, dimensions, and opening. The passage says Noah should make the vessel from gopher wood, cover it with pitch, and build it with three decks. Its stated dimensions are 300 cubits long, 50 cubits wide, and 30 cubits high.
Genesis 6 is also where God announces the coming flood and instructs Noah to preserve his family and representatives of living creatures. Genesis 7 then describes the animals entering and the flood beginning, while Genesis 8 covers the recession of the waters and the Ark’s resting place.
Readers sometimes associate the Ark’s measurements with Genesis 7 because that chapter narrates the flood itself. The actual dimensional specification appears earlier, in the construction instructions of Genesis 6.