U.S. Survey Foot

Putting the Best “Foot” Forward: Ending the Era of the U.S. Survey Foot (1959 to 2022)

Beginning on January 1, 2023, the U.S. survey foot should be avoided, except for historic and legacy applications and has been superseded by the international foot definition (i.e., 1 foot = 0.3048 meter exactly) in all applications. Prior to this date, except for the mile and square mile, the cable’s length, chain, fathom, furlong, league, link, rod, pole, perch, acre, and acre-foot were previously only defined in terms of the U.S. survey foot. With this update, relationships are available in terms of the international foot, which can simply be referred as the “foot.” Either the term “foot” or “international foot” may be used, as required for clarity in technical applications. This is particularly the case for surveying and mapping applications, although over time “foot” will become more prevalent. The preferred measurement unit of length in the United States is the meter (m) and surveyors, map makers, and engineers are encouraged to adopt the SI for their work.

Since 1893, the legal definition of the foot in the United States has been based on the meter. The definition adopted at that time was the one specified by Congress in 1866, as 1 foot = 1200/3937 meter exactly (or 1 foot = 0.304 800 6 meter approximately). In 1959, the relationship of the foot to the meter was officially refined as 1 foot = 0.304 8 meter exactly. This change was made to support United States industry and international trade. It resolved a long-standing discrepancy with the definition used by different organizations within the United States and in other countries.

The 1959 redefinition of the foot was legally binding and intended for the entire United States. But a single exception temporarily allowed continued use of the previous definition of the foot, exclusively for geodetic surveying. To distinguish between these two versions of the foot, the new one was named the “international foot” and the old one the “U.S. survey foot.” It was furthermore mandated that the U.S. survey foot be replaced by the international foot upon readjustment of the geodetic control networks of the United States. Although such a readjustment was completed in 1986, use of the U.S. survey foot persisted. This situation has led to confusion and errors that continue to this day, and it is at odds with the intent of uniform standards.

To resolve problems due to simultaneous use of two nearly identical versions of the foot, collaborative action is being taken by the National Institute of Standards and Technology (NIST) and the National Geodetic Survey (NGS), National Ocean Service (NOS), National Oceanic and Atmospheric Administration (NOAA). With the goal of providing national uniformity in the measurement of length, the U.S. survey foot will be phased out as part of the modernization of the National Spatial Reference System (NSRS). From this point forward, the international foot will be simply called the foot. A Federal Register Notice (FRN) was issued to solicit public comment to ensure that this change is made in an orderly fashion with minimal disruption and a final determination made to deprecate the use of the U.S. survey foot.