Area Unit Converter

Area unit converter allows you to quickly convert between different area units. It supports 18 common area units including metric units (square kilometers, hectares, ares, square meters, square centimeters), imperial units (square miles, acres, square yards, square feet, square inches), and traditional Chinese units (mu, qing). Whether for land surveying, real estate calculations, or everyday conversions, this tool provides accurate results instantly. All calculations are done locally in your browser, protecting your privacy. The important detail is unit context: square meters, square feet, acres, hectares, and regional land units are not interchangeable without careful conversion. Small rounding choices can become large absolute differences in construction, real estate, agriculture, flooring, mapping, and material estimates. This converter is best for quick calculation and comparison, while legal land records, engineering drawings, and procurement documents should specify precision, rounding rules, and the source unit clearly.

Area conversion is a closed-form arithmetic problem: every unit is a fixed linear scale of a reference unit (square metre under SI, square foot under US customary), so the page builds a directed graph of conversion factors and computes a path product between any two nodes. The graph edges are exact constants from NIST SP 811 (Appendix B) and the BIPM SI Brochure §2.3.3; for the imperial/US branch the constants are defined by the international yard and pound agreement of 1959, codified in NIST Handbook 44 for trade use. Within SI the math is exact powers of 10. Because area is a 2-dimensional quantity, the conversion factor between two linear units is squared: 1 m = 100 cm, so 1 m² = 10,000 cm², and 1 km = 1,000 m gives 1 km² = 1,000,000 m². The hectare (ha) and the obsolete are (a) are the two non-SI metric units accepted by the CIPM for land use: 1 ha = 10,000 m² (a 100 m × 100 m square, the practical size of a typical agricultural plot in 19th-century France where the unit was introduced in 1795), 1 a = 100 m². Both are powers of 10, so any conversion between SI area units is an exact multiply or divide without rounding. Imperial and US customary units are messier. The 1959 international agreement fixed 1 yard = 0.9144 m exactly, so 1 ft = 0.3048 m exactly and 1 ft² = 0.09290304 m² exactly. The acre is defined as 4,840 yd² (a furlong × chain: 1 fur = 220 yd, 1 ch = 22 yd, 1 acre = 1 fur × 1 ch = 220 × 22 yd²), giving 4,046.8564224 m² exactly. The US survey acre (used for legacy public-land-survey data, mostly in the western US) uses a slightly different foot (1 ft_survey = 1200/3937 m, because the original US definition predates the 1959 agreement), giving 4046.872609874252 m² — be careful when converting old USGS parcels. The survey township is 36 mi² (one survey township is exactly 36 sections of 1 mi² each). East Asian traditional units survive in mainland China, Taiwan, Japan, and Korea. The mainland Chinese mu (亩) was re-standardised to exactly 666.666... m² (one fifteenth of a hectare) in 1929 and again in 1959 with the metric transition. Taiwan's ping (坪) is 3.305785 m² (≈ 36 sq shaku, the shaku being 10/33 m). Korean pyeong (평) is the same as Taiwan's ping. The Japanese tsubo (坪) is twice the Taiwanese ping (≈ 3.305785 m² × 2 in some references, or 1 ken² = (1.818 m)² ≈ 3.3058 m² — same root constant), used for floor-area reporting under the Japanese Building Standard Act. Implementation detail: conversion between two units in this page is a single multiply by a precomputed constant, then a number-to-string with toPrecision(12) or a BigInt path for the integer-only chain. JavaScript's Number (IEEE 754 binary64) carries about 15-17 significant decimal digits, which is more than enough for land-area precision (the Earth's land area is ~149,000,000 km², fitting in 12 digits, and any practical parcel fits in 9 digits). For currencies, shares, or anything where exactness matters, use a decimal library like decimal.js — but for area, double precision is fine.

• Metric area conversions use the square of the linear factor: 1 m² = 10,000 cm² = 1,000,000 mm². Going from cm² to m² divides by 10⁴ (100²), not by 100 — every linear 10× becomes a 100× area factor.
• Hectare is a non-SI metric unit specifically designed for land measurement: 1 ha = 100 m × 100 m = 10,000 m². It is the standard unit for agricultural land in the EU, Australia, and most of Asia.
• The acre originated from the area a yoke of oxen could plow in one day; modern standard is 4,840 yd² = 4,046.8564224 m² exactly. The US survey acre is slightly larger (4046.8726 m²) and shows up in legacy public-land-survey parcels.
• 1 ft² = 0.09290304 m² exactly (international foot, 1959 agreement). The old US survey foot (1200/3937 m) gives a slightly different ft² and matters when reading pre-1959 deeds or USGS township data.
• Chinese mainland mu (亩) was standardised to 666.666... m² (1/15 ha) in 1929, reconfirmed in 1959. The qing (顷) = 100 mu ≈ 6.6667 ha. Both are powers-of-10 multiples of the hectare so conversions are exact.
• Taiwanese ping (坪) and Korean pyeong (평) are 3.305785 m²; Japanese tsubo (坪) and Korean pyeong in older references are about 3.3058 m² (one ken², with ken ≈ 1.818 m). These are the units used in property listings across East Asia.
• Conversion is a directed graph of edges labelled with the exact scale factor; the page picks a path, multiplies the factors, and returns the result in toPrecision(12) — never rounding twice, which is where most conversion bugs come from.
• Precision: JavaScript's Number (IEEE 754 binary64) gives 15-17 significant decimal digits, more than enough for any practical land parcel (Earth's land area is 1.49×10⁸ km², fitting in 12 digits). For infinite-precision needs, route through a BigInt or decimal library.