Size guide
Mu, hectare and square kilometre: converting land area correctly
Land area conversions fail for two reasons: the units are defined differently in different countries, and the numbers are rounded too early. This guide fixes the definitions first, then shows the formulas and the rounding rules that keep a land document consistent.
The units, defined
A mu (亩) is a Chinese market unit of land area. The modern definition is 1 mu = 666.666… m², or exactly 1/15 hectare. A hectare (ha) is 10,000 m². A square kilometre (km²) is 1,000,000 m², or 100 ha. An acre is 4,046.8564224 m², which is about 6.0703 mu.
Because mu is a repeating decimal of a square metre, any conversion that rounds mu to two decimals and then converts again will drift. Store the value in square metres, or keep at least four decimals in the intermediate step.
The formulas
m² to mu: divide by 666.6667. mu to m²: multiply by 666.6667. mu to ha: divide by 15. ha to mu: multiply by 15. km² to mu: multiply by 1500. mu to km²: divide by 1500.
A useful anchor is 1 ha = 15 mu. A 100 m × 100 m plot is 1 ha, or 15 mu. A 1 km × 1 km block is 100 ha, or 1500 mu. If a document says 0.6 ha, that is 9 mu, not 6 mu; the decimal is on the hectare, not the mu.
Where the errors come from
The most common error is mixing the mu/acre ratio with the mu/hectare ratio. An acre is about 6.07 mu, not 15 mu. Another common error is treating a “square” as a unit: a square metre is m², while a “square” in old property text may mean a square room or a square of roofing, not a fixed area.
Survey and subsidy documents often carry three or four decimals. Rounding 0.3333 ha to 0.33 ha changes the area by 33 m², which is material when the payment is per square metre. Keep the full precision until the final line, then round once and state the unit.
Checking a land document
Read the unit first, then the number. A deed may say 0.8 亩, 0.8 ha or 0.8 km²; those are three very different areas. Convert to m² as the common base, compare the result with the plot dimensions, and only then convert to the unit the recipient expects.
For a quick sanity check, a standard football pitch is about 0.714 ha (10.7 mu). A 100 m² apartment is 0.15 mu. If a conversion gives a number far outside these scales, the unit or the decimal point is usually the problem.
How to read the numbers in this guide
Values here are nominal. A manufacturer may allow a tolerance of a few tenths of a millimetre on a small part, or several millimetres on furniture and clothing, and an office may measure a photo print differently. Treat the table as a starting point, then confirm with the item or the authority that will receive it.
Conversions are rounded for display, but the calculation uses the full factor. Converting back can therefore return 0.999 or 1.001 instead of 1. When a decision depends on a threshold, work from the original unit rather than the rounded display value.
The guides are edited independently of advertising. An ad never changes a value or the order of a table. A correction is checked against the public standard and the data file, then the site is rebuilt, so the guide, the calculator and the category page show the same number.
Common questions
How many square metres is 1 mu?
666.6667 m², or exactly 1/15 ha.
How many mu in 1 hectare?
15 mu.
How many mu in 1 square kilometre?
1500 mu.
Is an acre the same as a mu?
No. 1 acre is about 6.0703 mu, or 4046.86 m².