The Bible describes the dimensions of the Noah’s ark, which reveal it to be a very large boat, even big enough to hold all the different “kinds” of animals on the earth.  The Bible describes the Noah’s ark as follows:

Genesis 6:14-16
"So make yourself an ark of cypress wood; make rooms in it and coat it with pitch inside and out. This is how you are to build it: The ark is to be 450 feet long, 75 feet wide and 45 feet high. Make a roof for it and finish the ark to within 18 inches of the top. Put a door in the side of the ark and make lower, middle and upper decks."

Often times, we see the ark shown as a curved, bath-tub shaped boat, with animals sticking their necks out of the windows.  Nothing could be further from the truth, or more misleading!  The ark was huge and was a large rectangular barge shape, which has been shown be a very stable design in high seas. 

The following picture show what the ark did NOT look like...

 

 And more likely what it actually appeared like:

 Source: www.answersingenesis.com

At 450 feet long, the ark would have been one and half times the length of a football field!  It would have been big enough to fit 569 railroad boxcars inside, which would be enough space to hold about 125,000 sheep, more than enough space for all the necessary animals!  Studies have determined that no more than 50,000 animals would have been required on the ark, and perhaps as few as 16,000.

 “Remember there are really only a few very large animals, such as the dinosaur or the elephant, and these could be represented by young ones. Assuming the average animal to be about the size of a sheep and using a railroad car for comparison, we note that the average double-deck stock car can accommodate 240 sheep. Thus, three trains hauling 69 cars each would have ample space to carry the 50,000 animals, filling only 37% of the ark. This would leave an additional 361 cars or enough to make 5 trains of 72 cars each to carry all of the food and baggage plus Noah's family of eight people. The Ark had plenty of space.” (http://www.christiananswers.net/q-eden/edn-c013.html)

For more information see:  1) Noah's Ark: A Feasibility Study, John Woodmorappe; 2)"The Genesis Flood," Morris and Whitcomb and 3) www.answersingenesis.com;  Interior painting of the ark from “The True Story of Noah's Ark” written by Tom Dooley; illustrated by Bill Looney