Square Mile

The square mile, commonly abbreviated as sq mi or mi², is a traditional unit of area used predominantly in the Imperial system and the United States customary system. It represents the area enclosed by a square with each side measuring one mile. Long established in land measurement and cartography, the square mile remains widely used in countries that retain non-metric units for administrative, legal, and geographical purposes.

Definition and Measurement Characteristics

A square mile is defined through the mile, a unit of length historically based on older surveying practices and now standardised as exactly 1,609.344 metres. By squaring this linear measure, the square mile provides a large unit of area suited to describing counties, cities, nature reserves, and other extensive geographic features. As an exponentiated unit, its magnitude far exceeds that of smaller customary units such as the square yard or square foot, making it especially appropriate for macro-scale measurement.
Within the traditional hierarchy of area units, a square mile can be broken down into 640 acres, each acre being a unit historically tied to agricultural land management. This relationship remains central to land valuation and property description in the United States and other regions employing customary measurements.

Equivalent Area Conversions

The square mile possesses several established equivalents within both the Imperial/US customary system and the metric system. These conversions allow interoperability across national and scientific contexts. Standard equivalences include:

• 1 sq mi = 4,014,489,600 square inches
• 1 sq mi = 27,878,400 square feet
• 1 sq mi = 3,097,600 square yards
• 1 sq mi = 640 acres
• 1 sq mi ≈ 2.58999 square kilometres

These values underpin routine operations in surveying, geospatial analysis, environmental assessment, and governmental land administration, where precise area measurement is essential.

Distinction Between Square Miles and Miles Square

A recurring source of confusion in measurement terminology concerns the distinction between square miles and miles square. Although similar in wording, these expressions describe fundamentally different concepts.

• Square miles refers to a measure of area, irrespective of the shape or proportions of the land. For example, any region with a total area of 400 square miles fits this description, whether its boundaries form a rectangle, an irregular shape, or a composite of multiple parcels.
• Miles square describes a region whose sides are each a specified number of miles in length. A region that is 20 miles square must form a square 20 miles on each side, thus having an area of 400 square miles. By contrast, a rectangle measuring 10 miles by 40 miles also has an area of 400 square miles but is not 20 miles square, as its sides differ in length.

The Section in United States Land Surveying

Within the United States Public Land Survey System (PLSS), the term section is frequently used as an informal synonym for the square mile. A section is defined as a parcel of land measuring one mile by one mile, thus encompassing one square mile. Sections form the basic units of a township, with each standard township consisting of 36 sections arranged in a 6 × 6 grid.
This system, established in the late eighteenth century, underpins rural land division and property identification across much of the United States, especially in states west of the original colonies. The square mile therefore continues to play a functional role not only in measurement but also in cadastral management, resource distribution, and rural planning.

Contemporary Uses and Significance

Despite the global prevalence of the metric system, the square mile remains a significant unit in many English-speaking countries for describing large areas. Its common applications include:

• mapping and describing political boundaries
• measuring land holdings, farms, and ranches
• reporting the size of counties, states, and national territories
• presenting ecological and population density statistics
• defining zoning classifications and planning districts