The Bible points out two lengths of the cubit, that shorter of 45,4(5) and that longer than a palm (7,4 cms) correspondingto 51,8 cms that appear in the measures of the temple of the Ezechiele vision. (Ez 40:5) Perhaps a third measure the shortest was also used, measured by the elbow to the knuckles of the closed hand of around 38 cms (Gdc 3:16)

It seems from the eyewitnesses that with the ark the longer cubit has been used. Insofar the measures would correspond to the sketch below: 

With a surface over 9000 mt2 and a capacity of around 60.000 mt3 cubes the ark would be able to contain around 800 railway wagons. (over 500 in the case of the short cubit of 44.4 cms) A couple of every animal that breathes air could be transported inside by only 150 wagons. It is esteemed that nowadays they are about 17.000 kinds of mammalian, amphibians, reptiles and birds, Calculating that the middle measure of such animals is comparable of a sheep, there would be not only space in the ark for two of every kind but thousand of kind it.