Why Are There 12 Inches in a Foot?

A foot (abbreviation ‘’ft’’) is a unit of length in the United States customary and imperial measurement systems. The international agreement defined both units as equivalent to 12 inches, and in both systems, a foot is equal to 12 inches, and a yard is made up of 3ft.

History of the Foot Measurment

Historically the "foot" was a part of numerous measurement system units which was included the English, French, Chinese, Roman and the Greek systems. The length of a foot varied from place to place, and it was either subdivided into 16 digit or 12 inches. The only industrialized country which uses the international foot instead of meters is the United States.

Previously, the basis of measurement was determined by the foot of a human being. In fact, the length of the foot of a white male is approximately 15.3% his height which means that the foot of a 5ft 3in tall man is about 9.65 inches long. These figures varied with time, therefore, suggesting that the unit "foot" was a synonym for an actual human-shoe. Archeologists suggest that the Mesopotamians, Indians, and Egyptians used cubit while the Greeks and Romans used a foot. To the Egyptians, 16 digits or 4 palms were equal to a foot. During the Bronze Age, most Indus towns used a foot which was approximately 13.2 inches.

First Usage of the 12-Inch Foot

The typical roman foot was approximately 11.64 inches which are about 97% of the measurements used today, but in the provinces the people used Nero Drusus’s foot (which was about 13.15 inches long). Initially, the Romans divided their foot into 16-digits, but they later split it into 12 unciae (which in English means ounce or inch). Jacob Koebel described the verification process of a foot during the 16th century.

The July 1959, international pound and yard agreement defined the international foot to be equivalent to 12 inches which were 1.7ppm (parts-per-million) shorter than the original United Kingdom definition and 2ppm shorter than that of the United States. In the United States, a foot was estimated to be 12 inches with an inch defined by the 1893 Mendenhall order which stated that one meter is equal to 39.37 inches.

Why 12 Instead of 10?

12 is a standard number and is used in the 12-hour clock, there are 12 months in a year, and 12 inches in a foot. But why use 12 instead of 10?

Historically not every nation had a 12-hour clock; in fact, the Egyptians were the only ones with a 12 hours for nighttime, 2 hours for twilight and 10 hours representing daytime. Therefore combining the 10 hour day and 2 hours for twilight equals 12 hours of night and day.

There are numerous speculations as to why they counted with the base of twelve and not 10 and this influenced different cultures over time. One of the schools of thoughts stipulates that our fingers have three joints and if you count the joints using our thumbs, we have twelve joints in both hands and this is how they counted.

The Babylonians developed a counting system known as the Sexagesimal system with a base of 60. The Sexagesimal system is used in counting time, and it has 12 factors. Plus mathematically 12 has more factors and is easier to subdivide as compared to 10. The 12-system of counting was adopted by many cultures including the Romans who introduced the idea of twelve inches in a foot.