US survey foot ft (US)
About the US survey foot
The US survey foot derives from the 1893 Mendenhall Order, which defined the US yard as 3600/3937 metres. When the 1959 agreement created the slightly shorter international foot, surveyors kept the old one to avoid altering land records. The difference of two parts per million adds up to about 3.2 mm per mile. NIST and NOAA deprecated the survey foot from 1 January 2023.
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