What this calculator does
This Area Unit Conversion Calculator takes a single area value and instantly expresses it in 16 different units across three families: metric (square millimeter, square centimeter, square meter, are, hectare, square kilometer), the yard-pound imperial/US system (square inch, square foot, square yard, rood, acre, square mile), and traditional Japanese land-area units (tsubo, se, tan, cho). It is a pure mathematical conversion tool that works anywhere; the Japanese units are simply included because they remain in everyday use for real-estate measurement.
How to use it
Enter the area value, choose the unit it is currently expressed in from the "Input unit" dropdown, and pick how many significant digits to display. The results table then lists the equivalent value in every supported unit. Negative and zero values are allowed and convert linearly (0 maps to 0 in all units).
The formula explained
Every unit has a fixed factor that converts one of that unit into square meters (the SI base). The tool first normalizes your input to square meters using the input unit's factor, then divides by each target unit's factor. So a value in unit A becomes a value in unit B via $$\text{Area} \times \frac{\text{factor}(A)}{\text{factor}(B)}$$ Imperial factors derive from the exact inch (\(1\ \text{inch} = 0.0254\ \text{m}\)): a square foot is \(0.3048^2 = 0.09290304\ \text{m}^2\) and an acre is \(43{,}560\) square feet \(= 4046.8564224\ \text{m}^2\). The Japanese tsubo uses the legal definition \(1\ \text{tsubo} = \frac{400}{121}\ \text{m}^2\) (one square ken), with \(\text{se} = 30\ \text{tsubo}\), \(\text{tan} = 300\ \text{tsubo}\) and \(\text{cho} = 3000\ \text{tsubo}\).
Worked example
For an input of \(1\) square meter, the calculator returns \(1{,}000{,}000\ \text{mm}^2\), \(10{,}000\ \text{cm}^2\), \(0.01\) are, \(0.0001\) hectare, \(1550.0031\) square inches, \(10.76391\) square feet, \(1.19599\) square yards, about \(0.000247105\) acre, and \(0.3025\) tsubo. These match the standard published conversion factors.
Area Unit Conversion Factors
The table below gives the exact (or exactly defined) value of each supported area unit expressed in square meters (m²). All conversions performed by the calculator are derived from these reference factors: to convert between any two units, multiply the input area by the source unit's factor and divide by the target unit's factor.
| Unit | Symbol / Name | Family | Value in m² |
|---|---|---|---|
| Square millimeter | mm² | Metric | 0.000001 |
| Square centimeter | cm² | Metric | 0.0001 |
| Square meter | m² | Metric | 1 |
| Are | a | Metric | 100 |
| Hectare | ha | Metric | 10000 |
| Square kilometer | km² | Metric | 1000000 |
| Square inch | sq in | Imperial / US | 0.00064516 |
| Square foot | sq ft | Imperial / US | 0.09290304 |
| Square yard | sq yd | Imperial / US | 0.83612736 |
| Rood | rood | Imperial / US | 1011.7141056 |
| Acre | acre | Imperial / US | 4046.8564224 |
| Square mile | sq mi | Imperial / US | 2589988.110336 |
| Tsubo (= 1 sq ken) | 坪 | Japanese | 400⁄121 ≈ 3.30578512 |
| Se | 畝 | Japanese | 12000⁄121 ≈ 99.17355372 |
| Tan | 段 / 反 | Japanese | 120000⁄121 ≈ 991.73553719 |
| Cho | 町 | Japanese | 1200000⁄121 ≈ 9917.35537190 |
Worked example: 1 acre converts to 4046.8564224 m². The imperial chain is exact: 1 sq ft = 0.09290304 m², 1 sq yd = 9 sq ft, 1 rood = 1210 sq yd, 1 acre = 4 roods = 4840 sq yd, and 1 sq mi = 640 acres. The Japanese units share the base \(1\,\text{tsubo} = 400/121\,\text{m}^2\) (= 1 square ken), with 1 se = 30 tsubo, 1 tan = 10 se = 300 tsubo, and 1 cho = 10 tan = 3000 tsubo.
FAQ
What is a tsubo? A tsubo is a traditional Japanese unit equal to a square ken (6 shaku by 6 shaku), about \(3.30579\ \text{m}^2\) or roughly two tatami mats, widely used for floor and land area.
How big is an acre versus a hectare? One acre is \(4046.8564224\ \text{m}^2\) and one hectare is \(10{,}000\ \text{m}^2\), so one hectare is about \(2.471\) acres.
Are the conversions exact? Yes. All factors are exact constants (the inch is defined as \(0.0254\ \text{m}\) and the tsubo as \(\frac{400}{121}\ \text{m}^2\)), so accuracy is limited only by the chosen display precision.
