A surveyor is at work near Niagara Falls, New York, in 1959, at about the time the U.S. government began the switch to the international foot. (AP)

A surveyor is at work near Niagara Falls, New York, in 1959, at about the time the U.S. government began the switch to the international foot. (AP)

Geodesist (one who measures the earth to determine exact coordinates of any point) Michael Dennis, in the foothills of South Mountain, in Laveen, Arizona. (AP)

Geodesist (one who measures the earth to determine exact coordinates of any point) Michael Dennis, in the foothills of South Mountain, in Laveen, Arizona. (AP)

Is your foot the same length as my foot? That depends not on shoe size, but on whether we use the survey foot or the international foot.

Is your foot the same length as my foot? That depends not on shoe size, but on whether we use the survey foot or the international foot.

Geodesist Michael Dennis of NOAA’s National Geodetic Survey holds a copy of the Manual of Surveying Instructions. (AP)

Geodesist Michael Dennis of NOAA’s National Geodetic Survey holds a copy of the Manual of Surveying Instructions. (AP)

A surveyor uses a transit while making land calculations.

A surveyor uses a transit while making land calculations.

A Foot Gets the Boot

Posted: March 2, 2020

How do you measure something as large as the United States? Measure by the foot, and use the official measuring stick. But there’s a problem. That stick is two different sizes. 

Some people measure land using the U.S. survey foot. It is a 12-inch measurement. Other people measure land using the international foot. It is also technically 12 inches. But really it’s a tad shorter. One stick, two sizes? It’s time for one foot to get the boot! 

The difference between the U.S. survey foot and the international foot is tiny. Don’t bother looking at a ruler. The difference is so small it’s pretty much invisible. It adds about an eighth of an inch for every mile. Think about how wide the United States is. Say you measure with the international foot. America will be 28.3 feet wider than when it’s measured with the survey foot. 

In 1959, U.S. government officials decided to stop using the survey foot. But the survey foot didn’t disappear. Some still measure land with it today. Others don’t. 

“This is a mess,” says Michael Dennis. He’s a land surveyor for the National Oceanic and Atmospheric Administration. He knows the chaos the two feet create. They made bridge work in Oregon and Washington messy. Oregon uses the international foot. Washington uses the U.S. foot. The feet caused trouble planning a high speed railroad in California. They wreaked havoc when a contractor put a building near an airport. Airport workers and the contractor used different sized feet to measure. The building ended up too close to the airport’s flight path. 

Why are the two feet different sizes? In 1893, the U.S. government defined a foot: 1,200 meters divided by 3,937. That makes the exact measurement of a foot 0.3048006 meters. In 1933, the international foot arrived. It was simpler. The last three digits were dropped. This foot measured 0.3048 meters, exactly. Think three digits don’t matter? Think again. 

In 2022, the U.S. survey foot will be history. Ever heard of the “cubit”? The cubit was about 18 inches, or around the length of six human palms. It’s another unit of measurement that became history—biblical history, that is. 

The house that King Solomon built for the Lord was sixty cubits long, twenty cubits wide, and thirty cubits high. — 1 Kings 6:2