Acres to Hectares Conversion Explained

What an acre and a hectare actually measure

Acres and hectares both describe the same thing: an area of land. An acre is a 43 560 square-foot rectangle (originally the area a yoke of oxen could plough in a day). A hectare is a square hectometre — 100 metres on each side, or 10 000 square metres. Different units, identical concept, and the acres to hectares converter moves between them using the exact factor 1 acre = 0.40468564224 ha.

The acre is the dominant land unit in the United States, Ireland, parts of South Asia, and informally across the United Kingdom. The hectare is the standard cadastral and agricultural unit across the European Union, Australia, New Zealand, Canada, China, and most of Africa and Latin America. The split is a legacy of the metric system's uneven adoption: countries that switched to SI by mid-century moved their land records with it, and the rest kept the imperial acre. Anyone reading an EU farm subsidy table, an FAO land-use report, or a UK Land Registry title plan needs the conversion at their fingertips.

The exact conversion math

The factor 0.40468564224 ha per acre is not an approximation. It comes from chaining two exact definitions. The acre is defined statutorily as 43 560 square feet, and under the 1959 International Yard and Pound Agreement the yard is exactly 0.9144 metres, so the foot is exactly 0.3048 metres. The Bureau International des Poids et Mesures (BIPM) defines the hectare as exactly 10 000 square metres. The ratio is the conversion factor:

1 acre = 43 560 ft² × (0.3048 m/ft)²
       = 43 560 × 0.09290304 m²
       = 4 046.8564224 m² exactly

1 ha   = 10 000 m² exactly

1 acre / 1 ha = 4 046.8564224 / 10 000
             = 0.404 685 642 24 ha per acre
1 ha / 1 acre = 10 000 / 4 046.8564224
             = 2.471 053 814 671 65 acres per hectare

Both numbers are exact rational fractions of integers — no rounding happens anywhere in the derivation. The only loss of precision is at display, where the acres to hectares converter rounds to ten significant figures. That is six orders of magnitude finer than any land survey can deliver, so for practical purposes the conversion is exact. NIST publishes the same factor in SP 811 (Guide for the Use of the International System of Units), and it appears unchanged in every UK Royal Institution of Chartered Surveyors (RICS) reference table.

A quick rule-of-thumb you can do in your head

Multiply acres by 0.4 to get hectares; multiply hectares by 2.5 to get acres. The error from using 0.4 and 2.5 instead of the exact factors is about 1.2% — perfectly fine for sizing up a farm at auction or sketching a plot on the back of an envelope. If you need more accuracy, use 0.405 (acres → ha) and 2.47 (ha → acres); both are within 0.05%. Common reference points worth memorising:

• 1 acre ≈ 0.4 ha — the canonical mental shortcut
• 2.5 acres ≈ 1 ha — the inverse shortcut, easier for hectare-first thinking
• 10 acres ≈ 4 ha — a smallholding
• 100 acres ≈ 40 ha — a small mixed farm
• 247 acres ≈ 100 ha (1 km²) — a substantial commercial farm
• 640 acres = 1 mi² ≈ 259 ha — one US Public Land Survey section
• 1 hectare ≈ 1.4 football pitches (the FIFA pitch is roughly 0.7 ha)

Worked example: a UK smallholding and a US ranch

A buyer comparing two listings on the same day — one in Devon, one in Montana — has to translate both into the same unit before comparing price per area. The UK listing reads "12.5 acres of pasture, two paddocks". The US listing reads "320 acres of grazing, single title". Convert both to hectares:

Devon: 12.5 acres × 0.40468564224 ha/acre
     = 5.058 570 528 ha
     ≈ 5.06 ha

Montana: 320 acres × 0.40468564224 ha/acre
       = 129.499 405 5168 ha
       ≈ 129.5 ha

The Montana property is 25.6 times larger by area. If the Devon plot lists at £85 000 and the Montana ranch at $480 000, the price per hectare comes out at roughly £16 800/ha versus $3 700/ha — a single comparable metric that imperial-vs-metric units would otherwise hide. Type either figure into the acres to hectares converter and flip the direction selector to verify the round trip lands back on the original number.

Going the other way: an EU farm subsidy form requires "area in hectares to two decimal places", but the title deed reads in acres. A 47.3-acre title becomes:

47.3 acres × 0.40468564224 ha/acre
            = 19.141 630 87... ha
            ≈ 19.14 ha

Two decimal places is well inside the precision the conversion can deliver. The same answer appears in the explanation panel of the acres to hectares converter, alongside the exact factor used.

Factors that change which unit you should use

Where the land sits

Jurisdiction wins. A UK Land Registry title plan post-2003 records area in hectares (Land Registration Rules 2003); pre-2003 titles often quote acres or hectares-and-acres in parallel. The US Bureau of Land Management's General Land Office records use acres exclusively, and Public Land Survey System (PLSS) descriptions still reference quarters of a 640-acre section. EU Common Agricultural Policy payments are calculated to four decimal places of a hectare. Match the unit on the source document and convert for comparison, not for record-keeping.

What the audience expects

Estate agent listings, hobby-farm forums, and US news articles default to acres because the readership thinks in acres. Scientific papers, EU policy documents, and most international agricultural statistics default to hectares for the same reason. A bilingual data table should show both, with hectares as the primary column when the source is metric.

What scale of decision is being made

For mental arithmetic on a viewing day, 0.4 and 2.5 are good enough. For a sale-and-purchase contract, use the exact factor. For boundary disputes or precise easement calculations, the conversion factor is the easy part — the hard part is the underlying survey, which a chartered surveyor or licensed land surveyor will quote to the nearest square metre or better.

Whether you are mixing in other area units

If a single document mixes acres, hectares, square metres, and square feet, do the conversions through a single SI bridge — pascals' equivalent for area is the square metre. The area converter handles m², ft², in², acres, hectares, and square miles in one tool; using it removes a class of bug where chained conversions accumulate rounding error.

Whether the survey vintage matters

Until 1 January 2023, the United States maintained two slightly different acres in parallel: the international acre (4 046.8564224 m² exactly) and the US survey acre (4 046.872 609... m²). They differ in the eleventh significant digit, about 16 mm² per acre. NIST retired the survey acre in 2023, and our converter uses the international definition. The only places where the survey acre still appears are historical PLSS records — and even there, the difference vanishes in any practical comparison.

How to convert acres and hectares without errors

• Always start from the document, not memory. Land titles and survey reports list the area to the precision the surveyor measured. Type that value into the acres to hectares converter rather than retyping a rounded figure.
• Pick a direction and stick to it. If your source is in acres, convert to hectares once and store the result; flipping back and forth multiplies the rounding error each round.
• Use two decimal places for general use, four for subsidy paperwork. Two decimals (0.01 ha = 100 m²) is sharper than any boundary fence; four decimals (0.0001 ha = 1 m²) matches the precision of a Common Agricultural Policy parcel declaration.
• Round at display, never mid-calculation. If you need a sum of three parcels, sum the unrounded hectares first, then round the total.
• Check the round-trip. If you convert 47.3 acres to hectares, then back to acres, the answer should land on 47.3 (within display precision). If it does not, you have an off-by-factor error somewhere — usually a forgotten ft²-to-m² conversion or a confused are vs. hectare.
• Verify the source unit. "Ha" in some old British texts means an "are" (100 m²), not a hectare (10 000 m²) — a factor of 100 difference. The hectare always carries the word "hectare" or the symbol "ha" unambiguously in modern documents.

Common mistakes

Confusing the acre and the are

The "are" (symbol "a") is an obsolete metric unit equal to 100 m². A hectare is 100 ares. A document that says "5 a" means 500 m² — about 0.124 acres, not 5 acres. The naming confusion is unforgiving: misreading a 12-acre listing as 12 ares would shrink it from about 4.9 hectares to 0.12 hectares, a forty-fold error.

Using the wrong acre

Pre-2023 US legal descriptions occasionally use the survey acre rather than the international acre. The difference is 4 ppm — about 16 m² in a square mile section. For almost every purpose the two are interchangeable, but if a deed is large enough or precise enough for that difference to matter, get a licensed surveyor's number, not a converter result.

Square units of different bases

Converting an area unit means squaring the linear conversion factor. 1 ft = 0.3048 m, so 1 ft² = 0.09290304 m² — not 0.3048 m². Anyone who linearly converts a square-foot figure to square metres ends up off by a factor of about 3.28. The same trap appears in any mixed-unit area: do the conversion through square metres, not through the linear units.

Treating "acre-foot" as an area

An acre-foot (used in US water rights) is a volume — 1 acre of area, 1 foot deep, about 1 233 m³. It is not an area. If a water-rights document says "10 acre-feet", that is a volume of water, not 10 acres of land surface.

When to seek professional advice

The conversion factor itself is exact, and the converter on this page is good to roughly 15 significant figures. The professional-advice threshold is not about the conversion; it is about the underlying area measurement. If a boundary is in dispute, if a sale hinges on a fraction of a hectare, if a tax or subsidy threshold sits inside the survey's margin of error, you need a chartered surveyor (UK, RICS) or licensed land surveyor (US, NSPS) to produce a measured plan from the cadastre or a fresh field survey. The converter takes their number and translates it; it does not produce the number itself.

Frequently asked questions

How many hectares are in an acre?

1 acre = 0.40468564224 hectares exactly. The factor is exact because both units have exact SI definitions: 1 acre = 43 560 ft² (statutory) and 1 ft = 0.3048 m exactly (1959 IYPA), and 1 hectare = 10 000 m² exactly (BIPM).

How many acres are in a hectare?

About 2.4710538147 acres. A hectare is a square 100 m on a side (10 000 m²), which is roughly 2.47 times the area of an acre. The mental shortcut "1 ha ≈ 2.5 acres" is correct to about 1.2%.

Is the US survey acre the same as the international acre?

They differ in the eleventh significant digit, about 16 mm² per acre. The international acre (used in the acres to hectares converter) is 4 046.8564224 m² exactly; the US survey acre, retired by NIST on 1 January 2023, was 4 046.872609... m². For practical conversion the difference is invisible.

How big is an acre in football pitches?

Roughly 0.57 of a FIFA-regulation football pitch. A standard FIFA pitch is 105 × 68 m = 7 140 m² = 0.714 ha = 1.765 acres, so one acre is about 57% of a pitch. A hectare is 1.4 pitches.

Why does a hectare equal 10 000 m²?

"Hecto" is the SI prefix for 100 and "are" is an obsolete SI-derived unit equal to 100 m². So 1 hectare = 100 ares = 10 000 m² by construction. Equivalently, a hectare is a square 100 m on a side (a square hectometre).

What is an acre in square metres?

Exactly 4 046.8564224 m². The conversion comes from 43 560 ft² × (0.3048 m/ft)² and is exact because both the foot and the acre have exact statutory definitions in SI base units. For square-metre conversions of other units, use the area converter.

Which countries use hectares and which use acres?

Hectares are standard in the EU, Australia, New Zealand, Canada, China, most of Africa, and most of Latin America. Acres are standard in the United States and informally in the United Kingdom and Ireland; UK Land Registry titles since 2003 record area in hectares even when the colloquial figure is in acres.

How accurate is the converter?

It uses the exact NIST/SI factor 0.40468564224 in IEEE 754 double precision. Round-trip error is below 1 part in 10¹⁵ — far below the resolution of any land survey. The only rounding happens in the displayed result.

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