What Is Square Mile (US Survey)?
A square mile US survey is a unit used to measure land area. It is based on the old United States survey mile. It is almost the same size as the normal square mile used today, but it is defined using the survey foot instead of the international foot.
You will mostly see the square mile US survey in American land surveying, old maps, and property descriptions, not in everyday life.
Definition
A square mile US survey is the area of a square where each side is one US survey mile long.
Important facts:
- 1 US survey mile = 5280 US survey feet
- 1 square mile US survey = (1 US survey mile) × (1 US survey mile)
- 1 square mile US survey ≈ 2.58999847 square kilometers
- 1 square mile US survey = 640 acres (survey based)
- 1 square mile US survey ≈ 27,878,403 square feet
- 1 square mile US survey ≈ 2,589,998.47 square meters
The square mile US survey is only slightly larger than the international square mile that is based on the international mile of exactly 1609.344 meters.
History / Origin
The square mile US survey comes from early systems used to measure land in the United States.
Main history points:
- In the 1800s the United States defined a special survey foot, built from a fraction involving meters, to keep old land records and new metric standards in line.
- From this survey foot came the US survey mile, and from that, the square mile US survey.
- Surveyors used it to lay out public lands, townships, ranges, and sections across much of the United States.
- In 1959 several English speaking countries agreed on the international yard and international foot. From that, the international mile and the international square mile were set.
- The US survey foot and the US survey mile stayed in use for land surveying because many maps and legal records already used them.
- In recent years, the United States moved toward using only the international foot, but old data and many legal descriptions still refer to survey based values.
Because of this long history, the square mile US survey still appears in technical and legal surveying work.
Symbol & Abbreviation
The square mile US survey does not have a single worldwide standard symbol, but these forms are commonly used:
- sq mi (US survey)
- mi² (US survey)
- sq mi (US), when the context is clearly survey based
In many documents, people simply write sq mi without saying “US survey”. In such cases, surveyors and engineers must check the context or the foot definition used to know which version is meant.
Current Use Around the World
Today, most countries use square kilometers and hectares for land area. The square mile US survey is very specialized and mostly limited to the United States.
Typical uses:
- Land surveying in the United States, especially where the Public Land Survey System is used.
- Legal land descriptions in deeds, titles, and property records that were created with survey feet and survey miles.
- Older maps and geospatial data, where the original work used US survey units.
Outside the United States, almost nobody uses the square mile US survey. Even in the US, most general news, school books, and maps use the international square mile or simply talk in square kilometers and acres.
Example Conversions
The square mile US survey is almost the same as the international square mile, so most everyday values are very close. Here are some example conversions using the survey based value.
- 1 square mile US survey ≈ 2.58999847 square kilometers
- 1 square mile US survey ≈ 258.999847 hectares
- 1 square mile US survey = 640 acres
- 1 square mile US survey ≈ 27,878,403 square feet
- 1 square mile US survey ≈ 3,097,600.4 square yards
- 1 square kilometer ≈ 0.3861022 square mile US survey
Difference compared to the international square mile:
- 1 square mile US survey ≈ 2.58999847 km²
- 1 international square mile ≈ 2.58998811 km²
- Difference ≈ 0.00001036 km², which is about 10.36 square meters
For simple everyday work this difference is tiny. For high accuracy mapping and legal work, the difference can matter, so the exact definition must be stated.
Related Units
Units closely related to the square mile US survey include:
- Square mile (international) The area of a square with sides of one international mile. Very close in size, but based on the international foot.
- Acre A common land unit. 1 square mile US survey equals 640 acres.
- Section In the US Public Land Survey System, one section is usually 1 square mile of land, traditionally based on survey units.
- Square foot (US survey) The square built on one survey foot. Used to define the survey mile and the square mile US survey.
- Square kilometer The main metric unit for large land areas. Widely used worldwide.
- Hectare Equal to 10,000 square meters. Often used for farms and forests. About 0.003861 square mile US survey.
FAQs
Q1. How is the square mile US survey different from the normal square mile?
The size is almost the same, but they are defined from different feet and miles. The US survey version comes from the survey foot, and the normal or international version comes from the international foot. The difference in area is about 10 square meters per square mile.
Q2. Why does the square mile US survey exist?
It exists because early United States land surveys used the survey foot and survey mile. To keep all those old records consistent, surveyors kept using the matching square mile based on those units.
Q3. Do I need to care about the difference for school or everyday life?
Usually no. In school or daily use, people can treat the square mile and the square mile US survey as the same. The small difference only matters for high accuracy work in surveying, mapping, or law.
Q4. How many acres are in one square mile US survey?
There are exactly 640 acres in one square mile US survey. This is the same number that people usually quote for a square mile.
Q5. Is the square mile US survey still officially used?
Modern standards in the United States prefer the international foot, but many existing land records, maps, and legal descriptions still rely on survey units. Because of that, the square mile US survey remains important for surveyors and for updating old data.
Q6. How do I know which type of square mile a map is using?
You must read the map notes or metadata. If it mentions the US survey foot, US survey mile, or uses older US land survey systems, it is likely using the square mile US survey. If it mentions the international foot or is from outside the United States, it almost always uses the international square mile or metric units.