Things You Didn't Know About the Foot
From ancient thumbs and barleycorns to airplane altimeters, the foot has a story worth telling
The foot is one of humanity's oldest units of measurement — quite literally based on the human body. But behind this seemingly simple unit lies a tangled history of royal decrees, international agreements, and a surprising role in modern aviation.
The Most Natural Unit
The foot is arguably the most intuitive unit of measurement ever devised. Unlike abstract standards based on Earth's meridian or the speed of light, the foot comes from something everyone carries: the human body. Ancient civilizations independently arrived at foot-based measurements because they were universally available — everyone has a rough measuring stick at the end of their leg.
The problem, of course, is that human feet vary enormously. A typical adult male foot ranges from about 240 mm to 300 mm. This is precisely why the "foot" meant different things in different places for thousands of years.
Ancient Feet Around the World
Every major ancient civilization had its own version of the foot, and none of them agreed:
| Historical Foot | Length (mm) | Length (inches) | Where Used |
|---|---|---|---|
| Egyptian foot | ~300 | ~11.81 | Ancient Egypt |
| Roman foot (pes) | ~296 | ~11.65 | Roman Empire |
| Attic/Greek foot (pous) | ~308 | ~12.13 | Ancient Athens |
| Olympic foot | ~320.5 | ~12.62 | Ancient Olympia |
| Carolingian foot | ~332 | ~13.07 | Frankish Empire |
| Paris foot (pied du Roi) | ~324.8 | ~12.79 | France |
| Rhenish foot | ~314 | ~12.36 | Prussia / Germany |
| Amsterdam foot | ~283 | ~11.14 | Netherlands |
| Castilian foot | ~278.6 | ~10.97 | Spain |
| Swedish foot | ~296.9 | ~11.69 | Sweden |
| English/Imperial foot | 304.8 | 12.00 | International standard |
The Roman foot (pes) deserves special attention. At approximately 296 mm, it was subdivided into 12 unciae — making the Romans the originators of the 12-division system that the English foot eventually inherited. Archaeological evidence for this length comes from graduated bronze rulers found at Roman sites, including one at the Temple of Juno Moneta.
The Paris foot (pied du Roi, meaning "the King's foot") was significantly longer than the English foot at 324.8 mm. It was divided into 12 pouces (inches), each pouce into 12 lignes (lines). Ironically, the pied du Roi was used as the basis for the meridian survey that originally defined the meter — the very unit that would replace it.
Barleycorns and Thumbs
How do you standardize something as variable as a human foot? Medieval England had a creative answer: barleycorns.
A statute from the reign of Edward II (early 14th century) defined the inch as the length of three barleycorns laid end to end, with 12 inches making a foot. This barleycorn definition persisted for centuries and — remarkably — is still the basis of British shoe sizes today. Each shoe size differs from the next by one barleycorn (roughly 8.5 mm or 1/3 of an inch).
The word "inch" itself comes from the Latin uncia, meaning "one-twelfth" — reflecting the Roman practice of dividing the foot into 12 parts. The connection to thumbs is preserved across European languages: the Dutch duim, French pouce, and Swedish tum all mean both "thumb" and "inch."
The 1959 Agreement That Settled Everything
For centuries, different countries used slightly different definitions of the foot. Even the American and British feet didn't quite match — the difference was about 2 parts per million, trivial for daily use but significant for geodetic surveys.
On July 1, 1959, the United States, United Kingdom, Canada, Australia, New Zealand, and South Africa jointly agreed to define the yard as exactly 0.9144 meters, making:
1 foot = 0.3048 meters exactly
1 inch = 25.4 millimeters exactly
This was a landmark moment — six nations agreeing on a single, precise definition tied to the metric system. The foot had finally been pinned down after thousands of years of variation.
The U.S. Survey Foot (1959–2023)
When the 1959 agreement was adopted, the United States kept the older, pre-1959 definition for geodetic survey work, calling it the U.S. survey foot:
| Definition | Value (meters) | Difference |
|---|---|---|
| International foot | 0.3048 exactly | — |
| U.S. survey foot | 1200/3937 ≈ 0.30480061 | +0.61 μm per foot |
The difference is about 0.61 micrometers per foot — roughly 3.2 mm per mile. Trivial for everyday use, but enough to matter when surveying entire states.
The U.S. survey foot was officially retired on January 1, 2023, when NIST and the National Geodetic Survey made the international foot the sole definition. A quiet end to a 64-year dual-standard era.
Why Pilots Worldwide Measure Altitude in Feet
One of the most striking examples of the foot's persistence is in aviation. Altitude is measured in feet worldwide — even in countries that are otherwise fully metric. A pilot in France, Japan, or Brazil reports altitude in feet and sets their altimeter in feet.
This convention dates to the early days of aviation, when the field was dominated by the United States and United Kingdom. The International Civil Aviation Organization (ICAO), established in 1944, adopted feet for altitude and knots for airspeed. By the time global civil aviation boomed in the postwar period, these conventions were already entrenched.
Standard cruising altitude for commercial aircraft is typically 31,000 to 42,000 feet (roughly 9,400 to 12,800 meters). Under Reduced Vertical Separation Minimum (RVSM), aircraft fly with just 1,000-foot vertical separation above FL290 — a system that only works because everyone worldwide uses the same unit.
Russia and China historically used meters for altitude but transitioned to feet for flight levels to align with ICAO standards — Russia in 2011, requiring retraining of thousands of controllers and pilots.
The Foot in Everyday Life
The foot quietly dominates several domains:
- Height: In the U.S., UK, Canada, and Ireland, people express height in feet and inches. "I'm 5-foot-10" is universally understood. Even in metric countries, older generations often think in feet for height.
- Real estate: Property in the U.S. and India is quoted in square feet, despite India being officially metric. A typical American single-family home is about 2,300 square feet.
- Construction: North American lumber is sold in foot-based dimensions — 8-foot, 10-foot, 12-foot boards. Ceiling heights are typically 8 or 9 feet.
- Shipping: Standard intermodal containers are 20 feet or 40 feet long. The TEU (Twenty-foot Equivalent Unit) is how container ship capacity is measured worldwide.
- Depth: Ocean depths are often given in feet — the Mariana Trench's Challenger Deep reaches approximately 36,070 feet (10,994 meters).
Feet by the Numbers
- 1 cubic foot = 1,728 cubic inches ≈ 28.3 liters ≈ 7.48 U.S. gallons
- A cubic foot of water weighs approximately 62.4 pounds (28.3 kg)
- The speed of sound at sea level is approximately 1,125 feet per second
- Light travels roughly 1 foot per nanosecond — an approximation accurate to about 2% that engineers use regularly
- Mount Everest stands at 29,032 feet (8,849 m), as confirmed by a 2020 joint Chinese-Nepalese survey
- The Statue of Liberty, base to torch, is 151 feet 1 inch tall; including the pedestal, 305 feet 1 inch
- A U.S. football field (excluding end zones) is 300 feet long
The Foot in Language
The foot is deeply embedded in English idioms — so deeply that we rarely notice:
- "Getting cold feet" — losing nerve before a commitment, possibly from soldiers unable to march with frostbitten feet
- "Putting your foot down" — asserting authority (also: pressing the accelerator)
- "Putting your best foot forward" — making a good impression (dates to at least the 16th century)
- "Foot in the door" — gaining initial entry, from the door-to-door salesman technique
- "Shooting yourself in the foot" — unintentionally harming your own cause (military origin)
- "One foot in the grave" — being very old or near death
- "Footprint" — now used metaphorically everywhere: carbon footprint, digital footprint
Who Still Uses the Foot?
The foot remains in active use in more places than you might expect:
| Country | Usage |
|---|---|
| United States | Primary unit for height, construction, real estate, aviation |
| United Kingdom | Height (feet/inches), aviation; roads use miles and yards but not feet |
| Canada | Height and construction, especially older buildings |
| India | Real estate (square feet), personal height — despite official metrication |
| Ireland | Informal use for height |
| Aviation worldwide | Universal unit for altitude in civil aviation |
The foot may be one of the oldest measurement units still in daily use. From a Roman bronze ruler to a 747's altimeter, it has proven remarkably difficult to replace — perhaps because it started where all good measurements do: with the human body itself.