A kilometer is 1,000 meters, but a square kilometer is 1,000,000 square meters: every area unit squares the ratio of its length unit. This area converter lists 39 units, from the electron cross section to the township, and keeps that rule visible.
A SQUARE MILE, TWO WAYS
By direct calculation with 50-digit arithmetic.
Area Converter
Complete list of area units
| Unit | 1 unit in square meters |
|---|
Shaded rows use the updated value of the panel on older tables. A red mark on the left shows units that share one value.
Definition: the Square Meter, the Hectare, the Acre and 39 Units
The square meter is the SI derived unit of area: the area of a square with sides of one meter, the meter being the distance light travels in 1/299,792,458 of a second. The hectare is a unit accepted for use with the SI, equal to 10,000 square meters. The acre is a unit of land area in the imperial and US customary systems, defined as the area of 1 chain (66 feet) by 1 furlong (660 feet), which is exactly 1/640 of a square mile, 43,560 square feet or 4,046.8564224 square meters. A square foot is the area of a square with one-foot sides, so it equals 144 square inches.
Around those anchors the converter lists the SI-prefixed square units, the survey versions of the mile, foot, acre and rod, land units such as the township, the section, the rood and the homestead, circular units, the barn, and traditional units named for other places, such as the arpent, the cuerda and the plaza. Five groups of units share one value, such as hectare and square hectometer, or square rod, square perch and square pole, which makes 33 distinct values behind 39 names.
History and Origin
Area is commonly represented as a square whose sides have a chosen unit of length, written as “square” followed by that unit. The square meter and the square foot both arise that way. The hectare was introduced in 1795 as part of the metric system, and its name combines the prefix “hecto”, a factor of one hundred, with the “are”, a metric unit of area that has fallen out of use in the SI but is still used in real estate, particularly in India, Indonesia and a number of European countries.
In the Middle Ages the acre was the area that a yoke of oxen could typically plow in one day with a wooden plow. Before the metric system, many countries had their own versions of the acre, and the international acre in common use today is based on the international yard, which was defined in 1959.
Current Use, and Two Acres
The square meter is most often used for land area such as rooms, houses and large plots, and its larger SI multiples are rarely used because the square meter is already sizeable. Hectares measure land area around the world, and their use is expected to continue indefinitely even though the hectare is only accepted for use with the SI. Acres are used in countries including the United States, the United Kingdom, Ghana, India and Canada. The square foot is used mainly in the United States and to some extent in the United Kingdom, Canada, Malaysia, Singapore, Pakistan, Bangladesh, India and Hong Kong, where real estate, architecture and interior spaces are often specified in square footage.
A square feet to square meters conversion multiplies by 0.09290304, and a square meter is 10.7639104167 square feet, so 15 square meters is 161.4586562506 square feet. A hectare to acres conversion multiplies by 2.4710538147, so 15 hectares is 37.0658072201 acres. An acres to square feet conversion multiplies by 43,560, and an acres to square miles conversion divides by 640. A township is 36 sections and a section is one square mile, so a township is 23,040 acres.
The United States uses both the international acre and the US survey acre, about 4,047 square meters, which vary with the type of yard used, although area measurements are typically not accurate enough for the difference to be detectable. The converter lists survey versions of the square mile, the square foot, the acre and the square rod. They are about 4 parts per million larger than their international counterparts: the survey acre is 4,046.8726098743 square meters, which is 0.0162 square meters more. NIST and the National Geodetic Survey deprecated the survey foot as of December 31, 2022.
Why Every Prefix Is Squared
A square hectometer is 10,000 times the size of a square meter even though a hectometer is only 100 times the size of a meter: the prefix applies to the side of the square, so the area changes by its square. The table gives the eight SI-prefixed square units of the converter.
| Square unit | Side, in m | Area, in m² |
|---|---|---|
| square kilometer | 1,000 | 1,000,000 |
| square hectometer | 100 | 10,000 |
| square dekameter | 10 | 100 |
| square decimeter | 0.1 | 0.01 |
| square centimeter | 0.01 | 0.0001 |
| square millimeter | 0.001 | 0.000001 |
| square micrometer | 10-6 | 10-12 |
| square nanometer | 10-9 | 10-18 |
Where Older Tables Are Out of Date
The electron cross section of the converter is the Thomson cross section, (8π/3) times the square of the classical electron radius. Older tables carry 6.6524616 × 10-29 m². NIST's 2022 table of the fundamental constants gives 6.6524587051 × 10-29 m², which is 0.44 parts per million lower and is the value this converter uses.
Frequently Asked Questions
How many square feet are in an acre?
Exactly 43,560, so an acre is 4,046.8564224 square meters.
How many square meters are in a hectare?
10,000, the same value as a square hectometer.
How many acres are in a hectare?
2.4710538147, so an acre is 0.4046856422 hectares.
How many square feet are in a square meter?
10.7639104167, which is 1 ÷ 0.09290304.
How many acres are in a square mile?
Exactly 640, which makes a section 640 acres.
Method and sources. Every factor was checked against its exact definition with 50-digit arithmetic. The status of the survey foot rests on a page relaying a federal notice, not on the primary NIST page.
This converter is provided for general reference. For surveying, real estate, legal or engineering work, use the unit and the standard the document specifies. Written by Staff Editorial, NumeraHub.