I believe that this was established by an English king at some point (probably around 1400's to 1500's). It is supposed that his foot was the measurement that was accepted as what we refer to as a "foot" (12 inches). The length of a foot today is not the same as it was when it was established, but it is probably pretty close.

It is said that Charlemagne's foot became the standard of length and that the width of his thumb—a space just one twelfth the length of his foot—was used as an inch (between 742 - 814 A.D.).

Before the Norman conquest of 1066 in Anglo-Saxon England, short distances were measured in a various of ways, such as: - The inch (ynce) - The shaftment - The foot & "natural foot" The inch was defined back then as the length of 3 barleycorns, which is very close to its modern length. The shaftment was roughly 6 1/2 inches long. The foot was equal to or about 12-inches, and the "natural foot" (pes naturalis) measured about 9.8 inches. The natural foot is believed to be based on an actual foot measurement. The Normans brought to England the Roman tradition of a 12-inch foot. It appears that during the reign of Henry I (1100 -1135) this 12-inch foot became official. Henry I also appears to have ordered construction of 3-foot standards, called "yards," establishing that unit for the first time in England. William of Malmsebury wrote that the yard was "the measure of his [the king's] own arm." This became the story that the yard was defined to be the distance from the nose to the fingertip of Henry I. In fact, both the foot and the yard were established from the Saxon ynce, the foot being 36 barleycorns and the yard 108. http://www.unc.edu/~rowlett/units/custom.html

The foot measurement was use way before any of the above. Noah was told to build a boat 450 feet long, 75 feet wide and 45 feet high at around 2400BC. And that was before the ancient Egyptians and Greeks were around and started using the measurement. Why is it larger than a human foot of today? Because humans were bigger: Genesis 6:4 There were giants in the earth in those days.

"The popular belief is that the original standard was the length of a man’s foot. In rural regions and without calibrated rulers, many units of measurement were in fact based on the length of some part of body of the person measuring (or for example the area that could be ploughed in a day). In that sense, the human foot was no doubt the origin of the measuring unit called a "foot" and was also for a long time the definition of its length. To prevent discord and enable trade, many towns decided on a standard length and displayed this publicly. In order to enable simultaneous use of the different units of length based on different parts of the human body and other "natural" units of length, the different units were redefined as multiples of each other, whereby their lengths no longer corresponded to the original "natural" standards. This process of national standardization began in Scotland in 1150 and in England in 1303, but many different regional standards had existed in both these countries long before. Some believe that the original measurement of the English foot was from King Henry I, who had a foot 12 inches long; he wished to standardize the unit of measurement in England. However this is unlikely, because there are records of the word being used approximately 70 years before his birth [4]. This of course does not exclude the possibility that this old standard was redefined ("calibrated") according to the ruler's foot. In fact, there is evidence that this sort of process was common before standardization. A new, important ruler could try to impose a new standard for an existing unit, but it is unlikely that any king's foot was ever as long as the modern unit of measurement. The average foot length is about 9.4 inches (240 mm) for current Europeans. Approximately 99.6% of British men have a foot that is less than 12 inches long. One attempt to "explain" the "missing" inches is that the measure did not refer to a naked foot, but to the length of footwear, which could theoretically add an inch or two to the naked foot's length. This is consistent with the measure being convenient for practical uses such as building sites. People almost always pace out lengths while wearing shoes or boots, rather than removing them and pacing barefoot. There are however historical records of definitions of the inch based on the width (not length) of a man's thumb that are very precise for the standards of the time. One of these was based on an average calculated using three men of different size, thereby enabling surprising accuracy and uniformity throughout a country even without calibrated rulers. It therefore seems likely that at least since about the Twelfth century, the precise length of a foot was in fact based on the inch, not the other way around. Since this length was fairly close to the size of most feet, at least in shoes, this enabled the above-mentioned use of one's shoes in approximating lengths without measuring devices. This sort of imprecise measuring that in addition excessively multiplied the measuring error due to repeated use of a short "ruler" (the foot) was never used in surveying and in constructing more complicated buildings." Source and further information: http://en.wikipedia.org/wiki/Foot_(length%29