Area Converter

Convert between metric and imperial area units (square millimetre, square centimetre, square metre, hectare, square kilometre, square inch, square foot, square yard, acre, square mile) with NIST-grade exact factors.

この計算機はまだ日本語に翻訳されていません。

翻訳作業中のため、英語版を表示しています。

From

Value

ft²

Result

0.092903 m²

1 ft²= 0.092903 m²

Decimals

All units

Unit	Value
Square millimeter (mm²)	92,903
Square centimeter (cm²)	929.03
Square meter (m²)	0.092903
Hectare (ha)	9.2903E-6
Square kilometer (km²)	9.2903E-8
Square inch (in²)	144
Square foot (ft²)	1
Square yard (yd²)	0.111111
Acre (ac)	2.29568E-5
Square mile (mi²)	3.58701E-8

更新日: 2026年5月19日

Area converter. Metric and imperial area units with NIST-exact factors.

An area converter translates a value from one unit of area to another using exact factors derived from the 1959 international yard and the SI metre. It pivots through the square metre, so square feet, square meters, acres, hectares, and square miles all round-trip without any conversion error.

What Is an Area Converter?

Every cross-border property listing eventually demands an area conversion: a 1,500 ft² US bungalow becomes a 139 m² apartment to a European buyer, a 5-acre Texas ranch reads as 2.02 ha to a Dutch agronomist, and a 90 m² Madrid flat translates to 969 ft² on a relocating American's spreadsheet. An area converter handles those translations without the off-by-one errors that creep into back-of-envelope multiplication. It is the calculator most often pulled up next to a real-estate listing, a building-permit application, a paint-coverage estimate, or a land-registry deed.

This converter handles those three audiences — real-estate, construction trades, and land surveyors — with the same engine. Every value is routed through a single base unit, the square metre, using each unit's defined factor: 1 square foot is exactly 0.09290304 m², 1 square inch is exactly 6.4516 × 10⁻⁴ m², 1 square yard is exactly 0.83612736 m², 1 acre is exactly 4046.8564224 m², 1 square mile is exactly 2,589,988.110336 m², and 1 hectare is exactly 10,000 m². These are not engineering approximations; they are exact rational factors that drop out of squaring the 1959 International Yard and Pound Agreement (which fixed the yard at exactly 0.9144 m) and from the SI definition of the hectare as a square 100 m on a side.

The converter supports ten units across two groups. The metric group (square millimetre through square kilometre, plus the hectare) dominates floor-plan listings in continental Europe, Latin America, most of Asia, and every EU/UK/AU/NZ land deed. The imperial group (square inch through square mile, plus the acre) dominates US, Canadian, Indian, Pakistani and several South-East Asian residential listings, plus US land deeds and Public Land Survey System sections. The two systems meet most often at the acre↔hectare boundary in farmland transactions and at the ft²↔m² boundary in floor-plan listings — both are exact in this calculator.

What distinguishes a serious area converter from a marketing widget is honesty about precision. The factor 1 m² ≈ 10.7639 ft² is not exact; it is a six-significant-figure rounding of the irrational quotient 1/0.09290304 = 10.7639104167…. The exact relationship runs the other way: 1 ft² is exactly 0.09290304 m². This calculator tags every result with an "exact" badge when both the source and target are defined by exact factors — which, for the area set, is every pair, because squaring an exact rational always yields another exact rational.

How to Convert Between Area Units

Every area conversion is one multiplication and one division through the square metre. The general formula is:

y = x \cdot \frac{a_{\text{from}}}{a_{\text{to}}}

where $x$ is your input value, $a_\text{from}$ is the source unit's factor to square metres, and $a_\text{to}$ is the target unit's factor to square metres. To do it by hand:

1. Look up the source-to-square-metre factor. For square feet, $a_\text{from} = 0.09290304$.

2. Multiply the input by that factor to get square metres. 1500 ft² × 0.09290304 = 139.35456 m².

3. Look up the target-to-square-metre factor. For square yards, $a_\text{to} = 0.83612736$.

4. Divide the square-metre value by the target factor. 139.35456 ÷ 0.83612736 = 166.666… yd².

The same procedure works for every supported unit. Going from acres to hectares: 5 ac × 4046.8564224 m²/ac ÷ 10000 m²/ha = 2.023428… ha. Going from square miles to square kilometres: 1 mi² × 2,589,988.110336 m²/mi² ÷ 1,000,000 m²/km² = 2.589988110336 km².

To use this calculator, pick the source unit from the "From" dropdown, type a value, then pick the target unit from the "To" dropdown. The result updates on every keystroke. Click the result card to copy it to the clipboard. Use the precision selector to switch between auto (6 significant figures), or a fixed 0, 2, 4, 6, 10 or 15 decimals. Auto-precision switches to scientific notation when the result is larger than 10¹² (one trillion) or smaller than 10⁻³, so converting a continent-scale area to square millimetres still renders readably. The "exact" badge appears next to every area result, because every unit in this set has a rational, definitionally exact factor to the square metre.

Area Conversion Formula

y = x \cdot \frac{a_{\text{from}}}{a_{\text{to}}}

$y$ = The converted value, expressed in the target unit of area.
$x$ = The input value, expressed in the source unit of area.
$a_{\text{from}}$ = Factor that converts the source unit to square metres (e.g. 0.09290304 for square feet, 4046.8564224 for acres).
$a_{\text{to}}$ = Factor that converts the target unit to square metres (e.g. 10000 for hectares, 0.83612736 for square yards).

The formula is a two-step pivot through the square metre base unit. The factor table this calculator uses is sourced directly from NIST SP 811 Appendix B.8 and derived from the 1959 International Yard and Pound Agreement and the SI definitions:

Square millimetre: 1 × 10⁻⁶ m² (exact, SI)
Square centimetre: 1 × 10⁻⁴ m² (exact, SI)
Square metre: 1 m² (exact, SI derived unit)
Hectare: 1 × 10⁴ m² = 10,000 m² (exact, SI-accepted non-SI; a square 100 m × 100 m)
Square kilometre: 1 × 10⁶ m² = 1,000,000 m² (exact, SI)
Square inch: 6.4516 × 10⁻⁴ m² = 0.00064516 m² (exact, squares of 0.0254 m)
Square foot: 0.09290304 m² (exact, squares of 0.3048 m; bolded in NIST SP 811)
Square yard: 0.83612736 m² (exact, squares of 0.9144 m)
Acre: 4046.8564224 m² (exact, = 4840 yd² by the 1959 yard)
Square mile: 2,589,988.110336 m² (exact, = 1609.344² m²)

For the m² → ft² direction the calculator displays the irrational quotient 1/0.09290304 = 10.76391041670972… ft²/m². Most casual converters print 10.7639 and stop there; this one will print as many digits as the precision selector requests, up to 15. The same applies to the hectare↔acre quotient: 10000 / 4046.8564224 = 2.4710538146716536… acres per hectare. It is irrational in form but tagged exact because both endpoints are defined by exact rationals.

Worked Area Conversion Examples

1,500 sq ft house plan to square metres

Set From = Square foot, To = Square meter, Value = 1500. The formula gives 1500 × 0.09290304 = 139.35456 m² exact. At auto-precision the result reads 139.355 m² (6 significant figures). Set precision to 10 decimals to see 139.3545600000 m². A typical US starter home listed as "1,500 sq ft" is right at the threshold between "compact" and "comfortable" in European listings, where the equivalent 139 m² home would be considered solidly mid-range. Both endpoints are exact, so this conversion has zero rounding error — the answer is mathematically exact, not just precise.

5 acres of farmland to hectares (real-estate cross-system)

Set From = Acre, To = Hectare, Value = 5. The formula gives 5 × 4046.8564224 / 10000 = 2.0234282112 ha exact. At auto-precision the result reads 2.02343 ha. This is the conversion every US-to-EU farm sale needs: a 5-acre US property maps to about 2 ha of European agricultural land. By comparison, a single English football pitch sits around 1.0 ha and an American football field is roughly 0.535 ha (without end zones). The result is tagged exact: both acre and hectare are defined by exact rational factors to the square metre.

1 hectare to acres (the constant every land owner memorises)

Set From = Hectare, To = Acre, Value = 1. The formula gives 10000 / 4046.8564224 = 2.4710538146716… acres. At auto-precision the result reads 2.47105 acres. This is the canonical metric-to-imperial land conversion: "one hectare is about two and a half acres". The quotient is irrational in form but tagged exact because both definitions are exact. For the back-of-envelope inverse, 1 acre ≈ 0.4047 ha (precisely, 0.40468564224 ha exact). Many land-registry systems in the EU, UK, Australia and New Zealand will print the hectare value to 4 decimals (10⁻⁴ ha = 1 m² resolution).

200 m² apartment to square feet

Set From = Square meter, To = Square foot, Value = 200. The formula gives 200 / 0.09290304 = 2152.78208334… ft². At auto-precision the result reads 2152.78 ft². This is a high-end European apartment by Spanish or Italian standards (the median is around 90–100 m²) but only a mid-large family home by US standards. The 10.7639 ft²/m² rule of thumb works for casual conversions, but if you are doing a CAD take-off or a building-code submission, take more digits — using 10.7639 instead of the exact 10.76391041670972 drifts by only about 0.01 ft² per 1000 m² of floor plan (invisible for any real-estate listing), but the coarser 10.76 rounding drifts by ~3.9 ft² per 1000 m², which starts to matter on warehouse-scale plans.

1 square mile to square kilometres

Set From = Square mile, To = Square kilometer, Value = 1. The formula gives 2,589,988.110336 / 1,000,000 = 2.589988110336 km² exact. This is why population-density figures shift dramatically when you cross the Atlantic: a US city quoted at "3,000 people per square mile" becomes "1,158 per square kilometre" in metric reports. The conversion is exact because both endpoints derive from exact factors (1 mi = 1609.344 m exact since 1959, so 1 mi² = 1609.344² m² = 2,589,988.110336 m² exact).

Comparative table: 1 unit in square metres

Unit	Value in m²	Equivalent in ft²	Equivalent in acres	Exact?
Square millimetre (mm²)	1e−6	1.0764e−5	2.4711e−10	yes
Square centimetre (cm²)	1e−4	1.0764e−3	2.4711e−8	yes
Square inch (in²)	6.4516e−4	6.9444e−3	1.5942e−7	yes
Square foot (ft²)	0.09290304	1	2.2957e−5	yes
Square yard (yd²)	0.83612736	9	2.0661e−4	yes
Square metre (m²)	1	10.7639	2.4711e−4	yes
Hectare (ha)	10,000	107,639	2.4711	yes
Acre (ac)	4,046.8564224	43,560	1	yes
Square kilometre (km²)	1,000,000	10,763,910	247.1054	yes
Square mile (mi²)	2,589,988.110336	27,878,400	640	yes

Two definitional shortcuts worth memorising: 1 acre = exactly 43,560 ft² (= 4840 yd²), and 1 mi² = exactly 640 acres (the "section" of the US Public Land Survey System). Both fall out of the same 1959 yard.

Most common area conversions

These are the unit pairs people look up most often. Use them as a quick reference, or paste them into the calculator for an exact result to 15 decimals.

Square metres to square feet: 1 m² = 10.7639 ft²
Square feet to square metres: 1 ft² = 0.092903 m²
Square metres to square yards: 1 m² = 1.19599 yd²
Square yards to square metres: 1 yd² = 0.836127 m²
Acres to square metres: 1 acre = 4,046.86 m²
Acres to square feet: 1 acre = 43,560 ft² (exact)
Hectares to acres: 1 ha = 2.47105 acres
Acres to hectares: 1 acre = 0.404686 ha
Hectares to square metres: 1 ha = 10,000 m² (exact)
Square kilometres to square miles: 1 km² = 0.386102 mi²
Square miles to square kilometres: 1 mi² = 2.589988 km²
Square inches to square centimetres: 1 in² = 6.4516 cm² (exact)
Square centimetres to square inches: 1 cm² = 0.155 in²

Area Conversion Tips

Pivot through the square metre, especially across the acre↔hectare boundary that drives most farmland sales. A 5-acre US ranch is 5 × 4046.8564224 = 20,234.282 m², which divided by 10,000 m²/ha is 2.02343 ha — the calculation every cross-border land conveyance walks through. The five exact factors worth memorising for this pivot are square inch (6.4516e-4), square foot (0.09290304), square yard (0.83612736), acre (4046.8564224) and square mile (2,589,988.110336), all defined exactly via the 1959 international yard.
Treat 10.764 ft² per m² as a back-of-envelope approximation. The exact relationship is the inverse direction: 1 ft² is exactly 0.09290304 m². Going the other way, 1 m² = 1/0.09290304 = 10.76391041670972… ft² is irrational and any printed value is a rounding. When you need engineering accuracy (CAD, building-code submissions, surveying), work in m² first and convert to ft² only at the end.
Memorise the two real-estate landmarks: 1 acre = 43,560 ft² and 1 hectare = 2.471 acres. Most US property listings quote lots under 1 acre in square feet (a typical US lot is 8,000–10,000 ft²) and lots ≥ 1 acre in fractional acres. EU/UK/AU/NZ land deeds quote hectares to four decimals (10⁻⁴ ha = 1 m² resolution). The 2.471 acres/hectare factor is irrational but tagged exact in this converter.
Use the precision selector to match your audience. Real-estate listings round to whole m² or ft² (a 139.35 m² apartment is advertised as "139 m²" or "1,500 sq ft", never with 4 decimals). Paint and flooring trades work to 2 decimals plus a 10% waste allowance — the 0.01 ft² rounding drift over 1000 m² from 10.7639 is dwarfed by cut-offs and pattern matching. Land surveyors and cadastral registries quote to 4 decimal hectares (10⁻⁴ ha = 1 m² resolution) for boundary stones. Engineers verifying a CAD take-off want 10 decimals; metrologists comparing against a primary standard want 15 (the full IEEE-754 double).
Every area unit in this set is exact. Unlike length conversions involving the light-year or parsec, where IAU definitions exceed 64-bit double precision, every area factor here is a finite rational number that fits cleanly in IEEE-754: 0.09290304, 0.83612736, 4046.8564224, 2,589,988.110336 — all exact. The "exact" badge fires for every pair, because squaring an exact rational always produces another exact rational.
Be careful with the US survey acre. NIST SP 811 lists the acre at 4046.873 m² because, until 2022, US federal agencies used the slightly larger US survey foot (1200/3937 m, about 2 ppm longer than the international foot). This calculator uses the international acre (4046.8564224 m² exact), which is the value used everywhere outside pre-2022 US federal geodetic survey work. The ~160 cm² (0.0166 m²) difference per acre — roughly the footprint of a tennis ball — matters for cadastral parity when comparing legacy US federal deeds to modern conveyances, but is invisible at any sub-metrology precision.
When the result is larger than 10¹² (one trillion) or smaller than 10⁻³ at auto-precision, the display switches to scientific notation. This is on purpose: writing 1 mi² in mm² as 2,589,988,110,336,000,000 mm² is unreadable, while 2.58999e18 mm² is parseable at a glance.
Confirm exactness when stakes are high. Cadastral surveying, land-purchase contracts and engineering tolerancing depend on knowing whether your conversion factor is a definition (no error) or a rounding (bounded error). NIST SP 811 Appendix B.8 prints the canonical list with exact factors in boldface; this calculator reproduces the same boldface-exact convention with the "exact" badge.
Square footage is not floor area only. In US real-estate listings, "sq ft" typically refers to heated (finished) interior space measured corner-to-corner, while the "lot size" is the parcel of land — often quoted in acres if larger than ~10,000 ft². Compare apples to apples before converting: an EU listing's "area" almost always means the same heated interior, not the lot.

Area Converter — Frequently Asked Questions

Is this area converter free?

Yes. The calculator is free, requires no account, runs entirely in your browser, and is ad-free. The embeddable iframe version at /widget/area-converter is also free and ad-free, so you can drop it into real-estate listings, construction-trade portals, school materials or technical blogs without exposing readers to third-party trackers.

How accurate are the area conversion factors?

Every factor in this converter is exact. The metric factors are exact by SI definition. The imperial factors (square inch, square foot, square yard, acre, square mile) are exact rationals derived from the 1959 International Yard and Pound Agreement, which fixed the yard at exactly 0.9144 m. NIST SP 811 Appendix B.8 prints the foot and inch factors in boldface to mark them as definitionally exact; the yard, acre and mile factors follow because squaring an exact rational stays rational.

How many square feet are in a square metre?

Exactly 1 / 0.09290304 = 10.76391041670972… ft² per m². The commonly quoted 10.764 is a five-significant-figure rounding. The exact direction is the inverse: one square foot is exactly 0.09290304 m², fixed by squaring the 1959 international foot (0.3048 m). For everyday work, 10.764 ft²/m² is enough; for CAD or building-code submissions, take more decimals.

How many square metres in one acre?

Exactly 4046.8564224 m². The international acre is defined as exactly 4840 square yards, and the 1959 yard is exactly 0.9144 m, so 4840 × 0.9144² = 4046.8564224 m². Equivalently, 1 acre = exactly 43,560 ft². The closely related US survey acre is about 4046.873 m² (about 160 cm² larger per acre — roughly the footprint of a tennis ball); this calculator uses the international acre, which is the global default.

Is a hectare bigger than an acre?

Yes. One hectare equals exactly 10,000 m², while one acre equals exactly 4046.8564224 m². So one hectare ≈ 2.4711 acres, or about two and a half acres. Conversely, one acre ≈ 0.4047 hectares.

What is the difference between an are and an acre?

They are completely different units. An are (a) is 100 m², a metric unit introduced in 1795 alongside the hectare (1 ha = 100 ares). An acre is 4046.8564224 m², an imperial unit derived from the 1959 yard. An acre is about 40.47 times larger than an are. The are is rarely used today outside Mexican land registers and a few European cadastres; the hectare and acre dominate land-area work.

How many square feet in an acre?

Exactly 43,560 square feet. The relationship is definitional: 1 acre = 4840 square yards = 4840 × 9 = 43,560 ft². Visually, that is roughly 90% of an American football field without the end zones.

How do I convert a room measurement to square footage?

For a rectangular room, multiply length × width in the same unit. A 16 ft × 12 ft bedroom is 16 × 12 = 192 ft². For metric work, a 5 m × 4 m bedroom is 20 m². If the room is L-shaped or irregular, split it into rectangles, compute each, and add. To convert the total to a different unit, enter the value in this calculator and pick the target. When ordering flooring or paint, the trade rule of thumb is to add 10% to your raw square footage as a waste allowance.

Why does 1 hectare to acres give an irrational decimal?

Because the exact definitions are on different sides of the metric/imperial fence. 1 ha is exactly 10,000 m² (a square 100 m × 100 m). 1 acre is exactly 4046.8564224 m². The quotient 10000 / 4046.8564224 = 2.4710538146716536… is mathematically irrational — there is no last digit, only a longer truncation. The calculator can print up to 15 decimals; most land-registry work uses 4.

How big is a square kilometre compared to a square mile?

A square mile is larger. 1 mi² = exactly 2.589988110336 km², or about 2.59 km². Equivalently, 1 km² ≈ 0.3861 mi². The relationship is exact because 1 mi = 1609.344 m exact since 1959, so 1 mi² = 1609.344² m² = 2,589,988.110336 m² exact, which divided by 1,000,000 m²/km² gives the 2.589988110336 figure. Most country-level land areas are quoted in km² in international datasets and mi² in US sources.

Can I embed this area converter on my site?

Yes. The embeddable version lives at /widget/area-converter; copy the iframe snippet from the embed page. The iframe is ad-free, dependency-free, mobile-responsive, and inherits no third-party trackers — useful for real-estate sites, construction-trade portals, and engineering education pages that need a converter without ad noise.

Why is the square foot factor 0.09290304 and not 0.0929?

Because 0.0929 is a four-significant-figure rounding. The exact factor is 0.3048² = 0.09290304, a finite rational that fits cleanly in 64-bit floating point. NIST SP 811 prints it in boldface as 9.290304 × 10⁻² to mark it as exact. The 0.0929 you see in casual references introduces an error of about 30 parts per million — invisible for a typical room measurement but accumulating to noticeable centimetres over a large floor plan.

Key Area Conversion Terms

Square metre (m²)

The SI derived unit of area, defined as the area of a square with sides of one metre. Since the 2019 SI revision the metre itself is fixed via the speed of light, so the square metre inherits that definitional precision. Wikidata: Q25343.

Hectare (ha)

A unit of area equal to exactly 10,000 m² — a square 100 m on a side. Introduced in 1795 as part of the metric system and listed in the BIPM SI Brochure as a non-SI unit accepted for use with the SI. It is the legal land-area unit across the European Union, UK, Australia, New Zealand and Canada. Wikidata: Q35852.

Acre (ac)

An imperial unit of area equal to exactly 4046.8564224 m² (= 4840 square yards = 43,560 square feet) under the international definition derived from the 1959 yard. Originally defined in medieval England as the area a yoke of oxen could plough in a day. Still the dominant land unit in the United States, India and Myanmar. Wikidata: Q81292.

Square foot (ft²)

An imperial/US-customary unit of area equal to exactly 0.09290304 m². Standard for residential real-estate listings and construction take-offs in the US, UK, Canada, India, Pakistan, Singapore, Malaysia and Hong Kong. NIST SP 811 prints the factor in boldface to mark it as definitionally exact.

Square inch (in²)

An imperial unit of area equal to exactly 6.4516 × 10⁻⁴ m² (= 0.0254² m²). Used in mechanical-engineering cross-sections, fastener bearing areas, and small surface measurements. 144 in² = 1 ft² exactly.

Square yard (yd²)

An imperial unit of area equal to exactly 0.83612736 m² (= 0.9144² m²). Common in carpet, textile and grass-pitch measurements. 9 ft² = 1 yd² exactly; 4840 yd² = 1 acre exactly.

Square mile (mi²)

An imperial unit of area equal to exactly 2,589,988.110336 m² (= 1609.344² m²). Used for US and UK regional and country-level land areas, population density, and as the basis of the US Public Land Survey System "section" (= 1 mi² = 640 acres exactly).

International Yard and Pound Agreement (1959)

Multilateral agreement signed by the US, UK, Canada, Australia, New Zealand and South Africa, effective 1 July 1959. It defined the yard as exactly 0.9144 m and the avoirdupois pound as exactly 0.45359237 kg. Every imperial area unit in this calculator (square inch through square mile) derives its exact metric value from this agreement.

Exact factor

A conversion factor fixed by international definition, with zero rounding error. For area, this includes 1 ft² = 0.09290304 m², 1 acre = 4046.8564224 m², 1 ha = 10,000 m². NIST SP 811 Appendix B.8 prints exact factors in boldface. Squaring an exact rational always yields another exact rational, so every area factor in this set is exact.

US survey acre

An obsolete US-only variant of the acre based on the pre-2022 US survey foot (1200/3937 m). Equal to about 4046.873 m², roughly 160 cm² (0.0166 m²) larger per acre than the international acre — about the footprint of a tennis ball. The US officially retired the survey foot effective 1 January 2023; modern US cadastral work uses the international acre that this calculator implements.

Significant figures

The digits in a numerical result that carry meaning about its precision. Auto-precision in this calculator targets 6 significant figures, the default for engineering tables. NIST SP 811 area factors are typically quoted to 7 significant figures so that any rational rounding of an exact factor is unambiguous.

Scientific notation

A way of writing very large or very small numbers as a coefficient times a power of ten, e.g. 1 mi² = 2.58999 × 10⁶ m². The calculator switches to this notation automatically when results fall outside the 10⁻³ to 10¹² range, so a continent-scale area in mm² remains readable.

出典・参考文献

Smart Calculators チームによる検証済みコンテンツ