The cubit is a unit of measurement that is approximately equal to 17.5 inches or 44.5 centimeters.
While the cubit was used by not only by Israel, but Mesopotamia and Egypt as well, a standard is difficult to find. It is defined as the length from the tip of the forefinger to the elbow. Each person would have a slightly different measurement according to this standard.
The tunnel of Siloam built by Hezekiah has been found with the inscription that is is 1200 cubits long. Upon measuring it, it is 1749 feet, giving us 17.49 inches per cubit, so 17.5 is a good approximation.
Noah’s ark is best known for being measured in cubits, coming in at 300 cubits long.
Related Definition: long cubit