“That the sacred Cubit was very large, appears from the Jewish Calamus or Reed, which contained but six of these Cubits; and from the antiquity of this Cubit, since Noah measured the Ark with it;” –Sir Isaac Newton 
“It is agreeable to reason to suppose, that the Jews, when they passed out of Chaldea, carried with them into Syria the Cubit which they had received from their ancestors. This is confirmed both by the dimensions of Noah’s ark preserv’d by tradition in this Cubit, and by the agreement of this Cubit with the two Cubits, which the Talmudists say were engrav’d on the sides of the city Susan during the empire of the Persians, and that one of them exceeded the sacred Cubit half a Digit, the other a whole Digit … The Roman Cubit therefore consists of 18 Unciæ, and the sacred Cubit of 25 3/5 Unciæ of the Roman Foot” –Sir Isaac Newton 
“The 25 inch cubit is found in ancient Egypt, Assyria, Persia, Syria, and probably in Greece, varying from 25.1 to 25.4. In modern Persia, Arabia, Greece, Candia, Algiers, and Italy, a pic or braccio of the same length is found, varying from 25.0 to 25.3. The possibility of this widespread unit having some connection with the Chinese foot (the double of which is 25.18 +/- .04) and with the North American mound builders’ foot (1/2 of 25.20 +/- .04) should not be disregarded; though farther evidence, beyond these very close resemblances, is needed to prove a connection. Don Quiepo also connects with it the Japanese inc 75.21–i.e., 3 x 25.07. … The Egyptian form of this cubit is probably nearest to the original, as being the oldest that we have, and this gives 25.10. This is well known as the sacred Hebrew, Royal Persian, and Chaldean cubit, mentioned by Newton, Golius, Kelly, Quiepo and Oppert.” –Sir William Matthew Flinders Petrie 
Answers in Genesis is building an ark. A full size one! See this link. I think this is a fantastic project and will be a tremendous educational tool. When I heard about the project, I checked to see what size cubit they were planning to use and it appears that the current plan is to use what some refer to as the Royal Egyptian cubit of around 20.7 inches. Make no mistake, AiG’s ark will be impressive at ~500 ft long if they use this cubit. But what if the cubit Noah used was really ~25 inches as the opinion of Sir Isaac Newton appears to be? Wow. That would make AiG’s ark 625 feet long! Even more impressive!
What is the evidence? Well, first we have Sir Isaac Newton’s research in which he makes the statements listed above. He lists 6 evidences from ancient literature supporting his belief that the sacred cubit was close to 25 inches long. Read more »