The United States spent more than a century with two feet in circulation. The international foot is exactly 0.3048 metres; the US survey foot is 1200 divided by 3937 metres, longer by about two parts per million. That is a difference of 0.6 mm over a thousand feet — trivial until it lands on a long boundary, a State Plane coordinate or a chain of title. This guide gives the exact numbers, explains what the 2023 deprecation actually changed, and sets out how to decide which foot a record used.
| Unit | Exact definition | In metres | Note |
|---|---|---|---|
| International foot | 0.3048 m | 0.3048 | Exact by definition; now the standard US foot |
| US survey foot | 1200 / 3937 m | 0.304800609601219… | Longer by 2 parts per million |
| Metre in international feet | 1 / 0.3048 | 3.2808398950 ft | |
| Metre in survey feet | 3937 / 1200 | 3.2808333333 ft | The inverse of the survey foot |
The survey foot came from the older definition of the metre as a physical bar, which made the inch-to-metre relationship an awkward fraction. When the metre was redefined in 1960 the awkwardness was resolved for science and industry by fixing the international foot at exactly 0.3048 m — but cadastral and geodetic records already existed in the old foot, and redefining them would have moved boundaries on paper. So both were kept, and the difference was named.
Two parts per million is the kind of number people round away without thinking, so it is worth seeing it accumulate in the units surveyors actually use.
| Length | Difference between the two feet | Practical reading |
|---|---|---|
| 1 foot | 0.0000006 ft (0.0000002 m) | Below any measurement |
| 100 feet | 0.00006 ft (0.02 mm) | Below any measurement |
| 1,000 feet | 0.0006 ft (0.2 mm) | Still below field precision |
| 1 mile (5,280 ft) | 0.0106 ft (3.2 mm) | Now visible on a good day |
| 1 UTM zone width (~668 km) | 4.0 ft (1.2 m) | Materially wrong |
| A 100-mile boundary | 1.06 ft (0.32 m) | A boundary dispute |
The pattern is the point: the error is invisible over a lot line and unavoidable over a county line. That is exactly the profile of a mistake that survives proofreading.
After a consultation that ran for several years, the US survey foot was formally deprecated for new work effective 1 January 2023, and the international foot became the standard foot in the United States. In practical terms this means that new federal and state work, and new National Geodetic Survey products, are defined in metres or international feet rather than survey feet.
What did not happen is any change to the records. A plat recorded in 1974 still describes the ground in survey feet; a State Plane coordinate published by a state agency in 1995 is still a survey-foot coordinate; a right-of-way plan from 2005 still bears survey-foot dimensions. The deprecation governs new work. It does not convert the archive, and it does not make the old numbers any less real. Anyone working with historic coordinates today — which, in cadastral practice, is most of the work — still needs the conversion.
Area is worse than length. A squared quantity carries the difference twice. The US survey acre — 43,560 survey feet squared — is 4,046.8726 m², against the international acre at 4,046.8564 m². Across a section, 640 acres, that gap is over 10 m² and it is not recoverable from the stated acreage alone.
| Conversion | Factor |
|---|---|
| US survey feet → metres | × 1200 ÷ 3937 = 0.304800609601219 |
| Metres → US survey feet | × 3937 ÷ 1200 = 3.280833333333 |
| International feet → metres | × 0.3048 |
| Metres → international feet | × 3.280839895013 |
| US survey feet → international feet | × 1.000002 |
That last factor is the one worth remembering, because it is close enough to 1 that it looks like nothing and far enough from 1 that it eventually matters. Multiply any survey-foot length by 1.000002 to get international feet.
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