Retirement of the US survey foot

It is well known that the USA uses miles, feet and inches and they are identical to the English versions of these units used in the UK. What is a lot less well known is the fact that the USA had two official feet, the international foot and the survey foot. By extension, there were also two versions of derived units based on these two feet. So there were survey and international versions of common units such as the mile, yard and inch. The US survey foot was deprecated at the end of last year. This deprecation act shows the importance of ensuring uniformity and common standards in measurement matters.

The USA decided to replace the customary standards of length based on those of England with length definitions based on metric units. The survey foot was introduced by the Mendenhall Order of 1893 when it was fixed as exactly 1200/3937 metres. When expressed as a decimal, a survey foot is approximately 0.3048006096 metres.

The international foot was introduced by agreement between several English-speaking countries, including the UK and USA, in 1959 to standardise the English foot worldwide at exactly 0.3048 metres. This eliminated the tiny differences in foot definitions between these countries. This was important for applications such as precision engineering, mutual compatibility of spare parts and interoperability of weapons systems between armed forces.

After 1959, the USA continued to use the survey foot for geodetic surveying but used the international foot for everything else. Thus the USA has had two official feet for over 60 years. Despite the fact that the difference between the two was less than 0.7 micrometres in length, it can lead to confusion and costly errors and delays for various types of projects. The elimination of the survey foot will reduce surveying errors that can cost money. For distances of hundreds or thousands of miles between co-ordinates, the difference between the survey foot and the international foot can add up to several feet.

For these reasons, the National Oceanic and Atmospheric Administration (NOAA), the National Ocean Service (NOS), the National Geodetic Survey (NGS) and the National Institute of Standards and Technology (NIST) decided to retire the survey foot at the end of last year and just use the international foot instead from 1 January 2023 onwards. The goal of deprecating the survey foot is to provide national uniformity of length measurements and resolve the problems with the simultaneous use of two versions of the foot with slightly different lengths. This is part of the modernisation of the National Spatial Reference System (NSRS).

In the Summary section of the Federal Register Notice (FRN) published by NIST and NOAA, it states:

“This notice announces the final decision to deprecate use of the “U.S. survey foot” on December 31, 2022. Beginning on January 1, 2023, the U.S. survey foot should not be used and will be superseded by the “international foot” definition (i.e., 1 foot = 0.3048 meter exactly) in all applications. The international foot is currently used throughout the U.S. for a large majority of applications and is typically referred to as simply the “foot.” Over time this terminology will become more prevalent in land surveying and mapping communities. Either the term “foot” or “international foot” may be used, as required for clarity in technical applications.”

In a nutshell, 31 December 2022 was the last day the US survey foot should be used and from 1 January 2023, the US survey foot is deemed obsolete and superseded by the international foot (also known as the foot) equal to 0.3048 metres exactly for all applications.

The standardisation of the foot measurement and its derivatives across the USA shows the importance of enforcing uniformity and common standards of measurement. The action taken by US federal agencies to eliminate survey measures should hold an important lesson for the British Government. This is a lesson the Government does not want to learn. It seems that the Government wants to go in the opposite direction by increasing the number of authorised units for trade and commerce.

Further reading:

2 thoughts on “Retirement of the US survey foot”

  1. A couple of minor corrections:

    First there is no Survey inch (and I am not sure about the yard) Surveyors use decimal feet, not feet and inches. However, all historic surveying terms, links, rods, chains, furlongs, as well miles and acres had two definitions. NGS does all their geodetic work in meters, but the states balked at metrication. The resolution was that NGS agreed to multiple these values by 3937/1200 or 1250/381, if the state defined in law which foot it intended to use. (8 states used the international foot, the rest, the survey foot.

    Second. the difference is mainly an issue in State Plane Coordinate Systems (SPSC), and release of new SPCS2022 is actually delayed until 2025. NGS has committed to supporting the Survey foot in legacy products for states that have been using the survey foot.

    NIST is deprecating it and changing how to refer to which foot is in use (the survey foot only for legacy applications). I have joked it is not dead yet, but is in hospice care.


  2. If you have 17 minutes of your life to spare, you can watch this video to learn how to convert from inches and fractions of inches, and feet and inches and fractions of inches to decimal inches or decimal feet, and how to check your calculations using three different types of imperial tape measure:

    “How to Convert Feet & Inches into Feet and Decimal Feet”

    Or, you could simply do all your measurements and work using the decimal metric system.

    Liked by 1 person

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