US Survey Foot vs International Foot: What Survey Drafters Need to Know

Two different "feet" are still in use in US survey data. The difference between them is tiny, but on state plane coordinates it can move a whole drawing by several feet. Here is what every survey drafter should know.

The two feet

• International foot: exactly 0.3048 meters.
• US survey foot: exactly 1200/3937 meters, about 0.3048006 meters.

The US survey foot is longer by about 2 parts per million.

The US survey foot was retired

In a 2020 Federal Register notice, NIST and NOAA's National Geodetic Survey announced the deprecation of the US survey foot, effective December 31, 2022. Since then the US survey foot is meant for historical and legacy data only, and the international foot is the standard foot in the US. For foot-based values, the new State Plane Coordinate System of 2022 uses the international foot.

That does not make old data disappear. Many existing projects, control networks and state plane coordinates (NAD 83 / SPCS 83) were produced in US survey feet, and you will keep receiving them for years.

When the difference matters

For distances on a single parcel, it rarely does. A 1,000-foot line differs by about 0.002 ft between the two units.

For coordinates, it can matter a lot. State plane coordinates are often in the millions of feet. At 2,000,000 ft, a 2 ppm difference is about 4 feet. If one dataset is read in the wrong unit, everything lands in the wrong place — and it can look almost right.

Signs of a unit mix-up

• Points from two sources that should match are offset by a few feet, by roughly the same amount and direction
• The offset grows the further you are from the origin of the coordinate system
• Distances between points look correct, but the points don't line up with control or imagery

How to avoid it in CAD

• Confirm the unit and coordinate system (zone and datum) for every dataset at the start of the job, and write it on the drawing.
• In Civil 3D, check the drawing settings: the coordinate zone and the imperial-to-metric conversion setting (US survey foot or international foot).
• When importing points, use the same unit settings as the data was collected in.
• Do not mix sources until they are confirmed to use the same unit and zone.

How Cadra handles it

Every job starts with an input check where we confirm units, coordinate system and datum with you, and flag any dataset that does not match before drafting starts.

Sources

• Federal Register — Deprecation of the United States (U.S.) Survey Foot
• NOAA National Geodetic Survey — Changes Afoot After 2022

Quick answers

What is the difference between the US survey foot and the international foot?+

The international foot is exactly 0.3048 m; the US survey foot is 1200/3937 m. The US survey foot is about 2 parts per million longer.

Is the US survey foot still used?+

It was deprecated effective December 31, 2022, but a lot of existing data and state plane coordinates are still in US survey feet, so drafters must check the unit of every dataset.