Genesis 6:19-21 tells us that Noah had to bring two of every sort of animal into the ark, as well as enough food for all of them and him and his family.  Would the ark have been big enough to have the proper amount of storage space for all of that?

The measurements of the ark, according to the Bible, was 300 cubits in length, 50 cubits in breadth, and 30 cubits in height, along with 3 decks (Gen. 6:15-16).  According to Brad Harrub’s book Convicted, in which he cites data from John Whitcomb and Henry Morris’s work The Genesis Flood, a cubit is generally thought to be about the length of your forearm, around 17.5 inches.  Thus, the total volume of the ark would have been about 1.39 million cubic feet of storage.

Additionally, consider this.  Ernst Mayer’s book, Principles of Systematic Zoology, proposes that Noah would have had to have provided space on the ark for 3,700 mammals, 8,600 birds, 6,300 reptiles, and 2,500 amphibians…a total of 21,100 different species.  Multiply that by 2 to get 42,200 different species of animal on the ark.  Add seven pairs of every kind of animal which God in the Old Testament would have considered to be clean for sacrificial purposes (Gen. 7:2-3), and the number would come to about 50,000.  The average size of these animals would be around the size of a sheep, considering that most of the birds, reptiles, and amphibians would have been smaller in size and other animals like cows and elephants would have been much larger.  So the question now is, could Noah have put 50,000 sheep-sized animals on the ark?

The ark had about 1.39 million cubic feet of storage, the carrying capacity of about 522 railroad boxcars.  It is estimated that one boxcar can hold 240 animals whose average size was of a sheep.  Thus, 125,000 animals could be placed into 520 boxcars.  If Noah had about 50,000 animals, then we conclude that the ark would have had plenty of room for all of them, with lots of room left over for eight people and the large quantity of food required for all of them.