Concise Bible Dictionary:
The vessel constructed by the command of God, by which Noah and his household and some of every living creature of the earth were saved when the world was destroyed by the flood. Precise instructions were given by God as to the construction of the ark. It was to be made of gopher wood, a kind known at the time, but which cannot now be identified with certainty; and it was to be pitched within and without with pitch, or bitumen, to make it water-tight.
Its proportions were to be 300 cubits long, 50 cubits broad, and 30 cubits high. If the cubit be taken at 18 inches, its length would have been 450 feet, its breadth 75 feet and its height 45 feet. If the cubit used had been 21 inches, the dimensions would be one-sixth larger.
A window was to be made to the ark (Gen. 6:16). The word tsohar signifies “a place of light” and was probably placed in the roof, and may have served in some way for ventilation as well as for giving light. Another word for window is used in Genesis 8:6 (challon) which could be opened from the inside. This word is used for the windows or casements of houses, and would give ventilation. In Genesis 6:16, after speaking of the window, it says, “and in a cubit shalt thou finish it above”; it is a question whether this refers to the size of the window or whether the word “it” refers to the ark. It has been said that the feminine suffix, which is rendered “it” cannot refer to the word window, which is masculine: so that it is possible the cubit refers to the roof; that the middle of the roof should be raised, giving a cubit for the pitch of the roof. A door was to be made in the side of the ark; and the ark was to be divided into three stories. “Rooms,” or “nests” (margin) are also mentioned (Gen. 6:14).
Such is the description given us of the form of the ark. It was by faith Noah prepared the ark, by which he condemned the world, and became heir of the righteousness which is by faith (Heb. 11:7). It is thus referred to in 1 Peter 3:20-21, “into which few, that is, eight souls, were saved through water: which figure also now saves you, [even] baptism, not a putting away of [the] filth of flesh, but [the] demand as before God of a good conscience, by [the] resurrection of Jesus Christ.”
It may just be added that the form of the ark was not intended for navigation amid storms and billows, but it was exactly suited for the purpose for which it was constructed. A ship for freight was once made in like proportions, to be used in quiet waters, and was declared to be a great success.
Various questions have been raised as to the veracity of the Bible account of the Deluge, for which see FLOOD.
Modern-Day Replica of the Ark—Ken Ham Creation Museum—Ark Experience