Foot (ft)
The foot is a unit of length in the imperial and US customary systems, equal to exactly 0.3048 meters or 12 inches. It remains the dominant unit for measuring human height, room dimensions, and building elevations in the United States and is still commonly used in the United Kingdom, Canada, and aviation worldwide.
Definition
One international foot equals exactly 0.3048 meters, 30.48 centimeters, or 304.8 millimeters. It is subdivided into 12 inches, and three feet make one yard. The US survey foot (1200/3937 meters) differs by about two parts per million and was used in American land surveying until its retirement in 2023, when NIST officially adopted the international foot for all purposes.
History
The foot is one of the oldest known units of measurement. Ancient civilizations including Egypt, Greece, and Rome each defined a foot based on the length of a human foot, typically ranging from 250 to 335 millimeters. The Roman pes (about 296 mm) spread across Europe and evolved into dozens of regional variants. England standardised its foot to approximately its current length by the 13th century. In 1959, the International Yard and Pound Agreement defined the foot as exactly 0.3048 meters, unifying the slightly different American and British definitions that had diverged over centuries.
Common Uses
In the United States, feet are used to express human height ("five foot ten"), ceiling heights, swimming pool depths, and lumber dimensions. Real estate listings describe floor area in square feet. Altitude in aviation is universally reported in feet, even in metric countries. In construction, architectural drawings and building codes throughout North America specify dimensions in feet and inches. The UK uses feet and inches informally for personal height while using meters for most official purposes.
Did You Know? Facts About Foot
- The foot was originally based on the length of a human foot, but King Henry I of England reportedly standardised it to the length of his own arm divided by three.
- Airline cruising altitude is reported in feet worldwide - a plane at 35,000 feet is at about 10,668 meters.
- The Statue of Liberty stands 305 feet (93 meters) from ground to torch tip, almost exactly 1,000 international feet if you include the pedestal and foundation.
- A standard basketball hoop is exactly 10 feet (3.048 meters) above the floor.
- The US survey foot was retired on January 1, 2023 after more than 130 years of use, ending a two-parts-per-million discrepancy with the international foot.