📖 Guide

Area Measurement: Acres, Hectares and the Roman Foot

The acre's medieval origin (one ox-team's day's plowing), why one hectare equals one square hectometer, and modern land measurement.

The Acre Has Roots in a Day's Work Behind an Ox

One acre is 43,560 square feet. That oddly specific number traces back to medieval England: an acre was the amount of land one ox and one plowman could till in a single day. The strip measured one furlong (660 feet) long and one chain (66 feet) wide. Multiply those and you get 43,560. The number survived centuries of metrication pressure because too much U.S. land law, agricultural regulation, and property deed language depended on it.

The tension between old and new measurements plays out every day. A Texas cattle rancher measures pasture in acres. A French farmer measures the same land type in hectares. A Bangladeshi rice grower uses bighas. All three measure the same physical concept: a two-dimensional surface. The units differ because each culture locked in a local standard before international coordination existed.

This guide covers the three major systems you will encounter: SI metric units (m², km², ha), U.S. customary units (sq ft, acres, sq miles), and the conversion factors that connect them. It also explains when each unit fits the task and why some professionals mix systems on the same project.

The Unit Systems and What Each One Covers

Area is length multiplied by width. Every area unit is therefore a length unit squared. Square meters (m²) come from meters. Square feet (sq ft) come from feet. That relationship matters when converting between systems, because you must square the linear conversion factor, not apply it once.

SI metric units build on one another in powers of ten. One square meter (m²) is a 1 m × 1 m square. One hectare (ha) equals 10,000 m², which is a 100 m × 100 m square. One square kilometer (km²) equals 1,000,000 m², or 100 hectares. The metric system uses hectares for land areas between field and country scale because they sit at a convenient human size: a standard soccer pitch is roughly 0.7 ha.

U.S. customary units run from tiny to vast. One square inch (sq in) is 6.452 cm². One square foot (sq ft) is 144 sq in or 0.09290 m². One square yard (sq yd) is 9 sq ft. One acre is 43,560 sq ft or 4,047 m². One square mile is 640 acres or 2.590 km². Real estate listings in the U.S. use square feet for buildings and acres for land parcels. Maps and census data use square miles.

The hectare spans both worlds. It is the SI-adjacent unit that metric countries use informally for agricultural land, because 1 km² is awkwardly large for a single farm field. France, Germany, and Australia measure farm fields in hectares. The U.S. Forest Service uses acres and hectares in the same reports.

Converting Between Systems: The Squaring Trap

The most common conversion error involves forgetting to square the linear factor. One foot equals 0.3048 meters. Therefore one square foot equals 0.3048² = 0.09290 m². Anyone who skips the squaring gets 0.3048 m², which is wrong by a factor of 3.28.

The conversions you will use:

1 sq ft = 0.09290 m²; 1 m² = 10.764 sq ft
1 acre = 43,560 sq ft = 4,047 m² = 0.4047 hectares
1 hectare = 10,000 m² = 107,639 sq ft = 2.471 acres
1 sq mile = 640 acres = 258.999 hectares = 2.590 km²
1 km² = 100 hectares = 247.105 acres = 0.3861 sq miles

Worked example: A property listing says 3.5 acres. A European buyer wants the size in hectares. Multiply: 3.5 × 0.4047 = 1.416 hectares. Reverse check: 1.416 × 2.471 = 3.50 acres. The cross-check confirms the result.

Second example: A warehouse floor plan shows 28,000 sq ft. A Canadian insurance form asks for m². Multiply: 28,000 × 0.09290 = 2,601 m². This equals 0.26 ha, or about 0.064 acres.

Common Misconceptions

A hectare is 1,000 m². A hectare is 10,000 m². The prefix "hecto" means 100, so one hectare is 100 m × 100 m = 10,000 m². Confusion arises from conflating it with the word "kilo."
An acre is roughly the size of a football field. An acre is 43,560 sq ft. An American football field including end zones is 57,600 sq ft. An acre covers about 76% of that. A soccer pitch ranges from 62,500 to 81,250 sq ft, so an acre is smaller than most soccer pitches too.
A square mile and a section are different things. In U.S. land survey terms, one section equals exactly one square mile (640 acres). They are the same unit described two ways. Thirty-six sections form one township (6 miles × 6 miles).
Converting sq ft to sq m requires dividing by 10. The actual factor is 10.764, not 10. Using 10 introduces a 7.6% error. On a 2,000 sq ft apartment, the quick-divide gives 200 m² instead of the correct 185.8 m².
Hectares are only used in Europe. Australia, Canada, South Africa, India, and most agricultural agencies worldwide use hectares. The U.S. is the main exception, though the USDA publishes crop data in both acres and hectares.

Worked Example: Buying Land Across Two Unit Systems

Anna converts a U.S. property listing for a European investor

Anna works as a real estate agent in rural Montana. A German investment group contacts her about a 4,800-acre ranch listed at $6.2 million. The investors think in hectares and want the price per hectare to compare with European farmland values.

Step 1: Convert acres to hectares. 4,800 × 0.4047 = 2,143 hectares.

Step 2: Calculate price per hectare. $6,200,000 ÷ 2,143 = $2,893 per hectare.

For reference, arable farmland in Germany trades around €25,000 to €45,000 per hectare (roughly $27,000 to $49,000 at 2024 exchange rates). The Montana ranch comes in at roughly one-tenth of German farmland prices, accounting for different land use and productivity.

The group also asks for the total area in km². Anna calculates: 4,800 acres ÷ 247.105 acres/km² = 19.4 km². That is a square roughly 4.4 km on each side. The investors can now compare it to landmarks they know from local geography.

Anna checks her work: 19.4 km² × 100 ha/km² = 1,940 ha. A small rounding difference from step 1 appears because she used a slightly different conversion path. Both figures confirm the ranch sits around 1,940 to 2,143 hectares, a range that collapses to a single answer when the same conversion factor runs through both steps.

When Standard Conversions Break Down

Survey feet vs international feet. The U.S. used the "survey foot" (1 survey foot = 1200/3937 meters) for land surveys until 2023, when NOAA retired it in favor of the international foot (0.3048 m exactly). Older property deeds may reference survey feet, which differ from the international foot by about 2 parts per million. Over large parcels the difference accumulates to centimeters.
Irregular shapes. Standard conversions assume you already know the area. Calculating area for an L-shaped lot or an irregularly shaped field requires decomposing the shape into rectangles or triangles, computing each sub-area, then summing before converting. Applying the conversion factor to a linear measurement and then computing the shape produces wrong results.
Sloped land. Survey measurements give horizontal (plan) area. A steep hillside covers more actual surface than its plan area indicates. Ecologists and engineers working with terrain need surface area, which requires GIS software or trigonometric adjustment based on slope angle.
Nominal vs net area in real estate. Building gross floor area (GFA) includes walls and common spaces. Net leasable area excludes them. Conversion calculators convert whatever number you input, so comparing one building's GFA in sq ft to another's net leasable area in m² produces a misleading result.
Country-specific units still in active use. India's bigha ranges from 1,500 m² to 6,770 m² depending on region. China's mu equals 666.7 m². Japan's tsubo equals 3.306 m². These units appear in land records that predate metrication and require local context before any conversion applies.

Quick Reference: Area Conversion Table

Unit	Equals in m²	Equals in sq ft	Equals in acres
1 m²	1	10.764	0.000247
1 sq ft	0.09290	1	0.0000230
1 are (100 m²)	100	1,076.4	0.02471
1 hectare	10,000	107,639	2.471
1 acre	4,047	43,560	1
1 sq mile	2,589,988	27,878,400	640
1 km²	1,000,000	10,763,910	247.105

Frequently Asked Questions

How many square feet are in an acre?

One acre equals exactly 43,560 square feet. The number comes from the medieval furlong (660 ft) multiplied by one chain (66 ft). The U.S. survey system standardized it, and it remains exact in law today.

How many acres are in a hectare?

One hectare equals 2.471 acres. One acre equals 0.4047 hectares. To convert acres to hectares, multiply by 0.4047. To convert hectares to acres, multiply by 2.471.

What does 1 hectare look like?

One hectare is a 100 m × 100 m square, totaling 10,000 m². It is roughly 1.4 times the area of an American football field including end zones, or about the size of a large city block in Manhattan. It equals 2.47 acres.

How do I convert square meters to square feet?

Multiply by 10.764. Example: a 75 m² apartment equals 75 × 10.764 = 807 sq ft. The common quick estimate of "multiply by 10" undershoots by about 7.6%, which matters when comparing listings across countries.

What is the difference between an are and a hectare?

One are equals 100 m², a 10 m × 10 m square. One hectare equals 100 ares, or 10,000 m². The "are" appears in older French and European property records but has largely been replaced by hectares in modern usage.

Why does the U.S. still use acres instead of hectares?

U.S. land law, property records, and agricultural policy have used acres for more than 200 years. The Public Land Survey System (PLSS) divided most of the western U.S. into sections of 640 acres each, creating hundreds of millions of legal documents that reference acres. Switching would require re-describing all of them.

How many acres are in a square mile?

One square mile equals exactly 640 acres. The U.S. township-and-range survey system divides land into townships of 36 square miles, each square mile being one section of 640 acres. Ranches and counties in the western U.S. are still commonly described by section count.