All Area Units

How to Convert Area Units?

Area conversion is essential for real estate, land surveying, construction, and agriculture. This converter handles both metric and imperial area units using precise mathematical relationships. Enter any area value, select your source unit, and instantly convert to square meters, square feet, acres, hectares, and more.

Frequently Asked Questions

What units of area does this converter handle?

This converter handles SI metric units (square millimeter, square centimeter, square meter, hectare, square kilometer), US customary units (square inch, square foot, square yard, acre, square mile), and a few specialized survey/agricultural units. The square meter is the SI derived unit, defined as the area of a square with sides of 1 meter (the SI base unit of length). The hectare is exactly 10,000 m^2 and the are is exactly 100 m^2; both are non-SI but accepted for use with the SI by the BIPM. The acre and square mile derive from the international yard (1 yd = 0.9144 m exactly since 1959), making all conversions exact rational numbers.

What are the exact conversion factors for area?

1 hectare = exactly 10,000 m^2 = 100 ares = 0.01 km^2. 1 acre = exactly 4046.8564224 m^2 (from 1 acre = 43560 ft^2 and 1 ft = 0.3048 m exactly). 1 square mile = exactly 2,589,988.110336 m^2 = 640 acres = 2.589988110336 km^2. 1 square foot = exactly 0.09290304 m^2. 1 square inch = exactly 6.4516 cm^2 = 0.00064516 m^2. Note 1 hectare is approximately 2.471 acres, and 1 km^2 is approximately 247.1 acres or 0.386 sq mi. All factors come from the 1959 international yard agreement; the older US Survey Foot (0.3048006096 m, retired 2022) is 2 ppm larger and would give acres about 0.0006% different - usually negligible but critical in legal surveying.

When should I use m^2, hectares, or square kilometers?

Use square meters for rooms, building floor areas, small plots (less than ~5000 m^2), and most engineering. Use hectares (ha) for farmland, parks, forests, vineyards, urban land-use planning, and properties from 1 to 1000 ha; this is the dominant agricultural unit globally outside the US/UK. Use square kilometers (km^2) for cities, regions, countries, lakes, and large geographic features. As a rule of thumb: house plot = m^2, farm field = ha, country = km^2 (Vietnam is 331,212 km^2 = 33.1 million ha). For sub-square-meter areas (electronics, textiles, paper), use cm^2 or mm^2.

How precise are the conversions and what rounding is right?

All factors are exact rational numbers derived from the 1959 international yard, so conversions are decimal-exact internally to 15+ significant figures. In practice, area measurements rarely justify high precision: surveyor-grade total stations measure plots to ~1 ppm but the original boundary descriptions often have +/-10 cm at corners. For real estate, 3 to 4 significant figures suffice (a 1234.5 m^2 lot, not 1234.567 m^2). For agriculture, 0.01 ha precision is the norm (one tenth of a hectare equals 1000 m^2 = 0.25 acres). For ecology and geography, 2 to 3 significant figures match the inherent measurement uncertainty.

What are common area gotchas?

First, the US Survey vs International yard before 2022: US Survey Foot was 0.3048006096 m, International is exactly 0.3048 m, leading to area differences of about 4 ppm. Property deeds in some US states may still reference Survey Feet. Second, 'square feet' in real estate can mean gross, rentable, usable, or carpet area - each defined differently and ambiguity is common. Third, 'acre' has two definitions: the international acre (4046.8564224 m^2) and the survey acre (4046.872609874252 m^2). Fourth, the are (10x10 m) vs the hectare - the are has fallen out of use except in some old land titles. Fifth, 'sq m' vs 'm sq' vs 'm^2' all mean the same thing despite typographic variation.

What is the relationship between area, surface area, and projected area?

Area is the planar two-dimensional measure of a region in m^2. Surface area is the 2D measure of a 3D object's outer boundary, also in m^2 (a sphere of radius r has surface area 4*pi*r^2). Projected area (or 'shadow area') is the 2D outline when an object is projected onto a plane; aerodynamic drag uses frontal projected area. For a roof, the 'projected area' is the floor plan footprint, while the 'roof surface area' includes slope and is larger by 1/cos(slope angle). For solar panels, energy received scales with the area perpendicular to the sun's rays, not the panel's geometric surface. The converter handles pure planar area; geometric and projected adjustments are your responsibility.

How is the square meter defined in the modern SI system?

The square meter is an SI coherent derived unit equal to m^2, where the meter is defined since 2019 as the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second (with the second defined by caesium frequency). The meter definition is exact: the speed of light c is fixed at exactly 299,792,458 m/s by definition. Therefore the square meter is realized via laser interferometry to fractional uncertainty better than 10^-12. National metrology institutes (NIST, NPL, PTB) maintain primary length standards. The BIPM coordinates international comparisons. For everyday surveying, GPS achieves ~1 cm precision over ~1 km baselines, easily good enough for cadastral work.

What are area edge cases at extreme scales?

Very small areas: atomic cross-sections are measured in barns (1 barn = 10^-28 m^2); a single human cell membrane is roughly 10^-9 m^2; a transistor on a 7-nm chip is roughly 10^-15 m^2. Very large areas: the surface of the Earth is 510 million km^2 (510 trillion m^2); the Sahara Desert is 9 million km^2; Russia is 17.1 million km^2; the Sun's surface is 6 trillion km^2. The converter handles arbitrary magnitudes mathematically. For geodesy, note that 'flat' Earth area calculations fail above ~100 km^2; you need spherical or ellipsoidal corrections. For solar-system or astronomical areas, you exit standard units and use AU^2 or pc^2 instead - the converter does not cover these.

Square Meter (m²)

The square meter is the SI derived unit of area. It represents the area of a square with sides of one meter. Square meters are used worldwide for measuring floor space, land plots, and surfaces in construction, real estate, and scientific applications.

Square Foot (ft²)

The square foot is a unit of area used primarily in the United States and United Kingdom. One square foot equals 0.0929 square meters or 144 square inches. It's the standard unit for real estate listings, home sizes, and commercial spaces in these countries.

Acre

The acre is a unit of land area used in the US and UK. One acre equals 43,560 square feet, 4,047 square meters, or about 0.4047 hectares. It's commonly used for measuring farms, parks, and large land parcels. Originally defined as the area a yoke of oxen could plow in one day.

Hectare (ha)

The hectare is a metric unit equal to 10,000 square meters or about 2.471 acres. It's the standard unit for measuring agricultural land, forests, and large properties in most countries. One hectare is roughly the size of a standard soccer field.

Square Kilometer (km²)

The square kilometer equals one million square meters or about 0.386 square miles. It's used for measuring cities, countries, lakes, and other large geographic areas. One square kilometer contains 100 hectares.

Common Area Conversions