Acre (acre) - Unit Information & Conversion

Definition

The acre (symbol: ac) is a unit of land area used in the imperial and US customary systems. It is traditionally defined as the area of one chain by one furlong (66 by 660 feet). This is exactly equal to:

• 10 square chains
• 1/640 of a square mile
• 4,840 square yards
• 43,560 square feet
• Approximately 4,046.856 square meters (m²)
• Approximately 0.4047 hectares (ha)

While derived from traditional farming practices, its size is now legally defined based on the international yard.

History

• Origin: The word "acre" derives from the Old English word æcer (originally meaning "open field"), cognate with German Acker and Latin ager. It traditionally represented the amount of land that could be ploughed by one man with one yoke of oxen in one day. This practical definition naturally led to considerable variation in its size depending on the land quality and local customs.
• Medieval Variations: Throughout the Middle Ages in England, the acre's size varied. Different regions used "customary acres" based on local practices, often related to the quality of the land or the length of a standard furrow (furlong).
• Standardization (Gunter's Chain): The standardization of the acre is closely linked to the invention of Gunter's chain in 1620. This measuring chain, 66 feet long (divided into 100 links), became a standard survey tool. The traditional definition of an acre as a strip of land one furlong (10 chains or 660 feet) long and one chain (66 feet) wide was easily measured using the chain. This area is precisely 10 square chains.
• Statutory Acre: In England and Wales, the Weights and Measures Act of 1878 formalized the "statutory acre" based on the imperial yard, solidifying the definition as 4,840 square yards (or 43,560 square feet). This is the acre commonly used today in the UK, US, and Commonwealth countries.
• Metrication: Although many countries using the acre have largely adopted the metric system for other measurements, the acre persists strongly in land transactions and agriculture due to historical precedent and cultural familiarity. The hectare (10,000 m²) is the more common metric unit for land.

Common Uses

The acre remains a primary unit for land measurement in several countries, particularly within specific sectors:

• Real Estate (US, UK, Commonwealth): Standard unit for describing the size of land parcels in property listings, deeds, and surveys, especially for residential lots larger than typical city plots, rural properties, and undeveloped land.
• Agriculture: Widely used by farmers to measure field sizes, calculate crop yields, allocate resources (like fertilizer or seeds), and comply with agricultural regulations.
• Land Management and Planning: Used in zoning regulations, environmental assessments, and land development projects to specify area requirements or limitations.
• Historical Documents: Understanding the acre is crucial for interpreting historical land records, surveys, and deeds.
• Informal Comparisons: Often used informally to help visualize the size of large areas, even where metric units are officially standard.

Unit FAQs

How big is an acre visually?

An acre is 43,560 square feet. While it can be any shape, a square acre would be about 208.71 feet on each side. A common visual comparison is an American football field: one acre is about 90.75% of the total area of a standard American football field (which is 120 yards long by 53.33 yards wide, or 57,600 sq ft including end zones). Excluding the end zones (100 yards by 53.33 yards, or 48,000 sq ft), an acre is about 90.75% of the playing field area.

How many square feet are in an acre?

There are exactly 43,560 square feet in one acre. This definition (1 furlong × 1 chain = 660 ft × 66 ft) is precise.

How many square yards are in an acre?

There are exactly 4,840 square yards in one acre (since 1 yard = 3 feet, 1 square yard = 9 square feet; 43,560 / 9 = 4,840).

How many acres are in a square mile?

There are exactly 640 acres in one square mile.

How many acres are in a hectare?

One hectare is equal to 10,000 square meters. Since one acre is approximately 4,046.856 square meters, one hectare contains approximately 2.471 acres (10,000 / 4046.856 ≈ 2.471). Conversely, one acre is approximately 0.4047 hectares.

Is the acre an SI unit?

No, the acre is not part of the International System of Units (SI). It belongs to the imperial and US customary systems. The SI unit for area is the square meter (m²). For land measurement, the hectare (ha), equal to 10,000 m², is commonly used in metric contexts and is accepted for use with SI.