### Metric system

square millimeter | mm^{2} | |

square centimeter | cm^{2} | |

square meter | m^{2} | |

are | a | |

hectare | ha | |

square kilometre | km^{2} |

### United States customary units / Imperial units

square inch | sq.in. | |

square foot | sq.ft. | |

square yard | sq.yd. | |

rood | ro | |

acre | ac | |

square mile | sq.mi. |

### Japanese units of measurement

shaku | 勺 | |

gō | 合 | |

tsubo | 坪 | |

se | 畝 | |

tan | 反 | |

chō | 町 | |

jō | 畳／帖 |

A number with many digits may appear as "1e9". This is the computer's exponential representation, where "e" is a power of 10.

1e3 = 10

^{3}= 1,0001e6 = 10

^{6}= 1,000,0001e9 = 10

^{9}= 1,000,000,0001e-3 = 10

^{-3}= 0.0011e-6 = 10

^{-6}= 0.0000011e-9 = 10

^{-9}= 0.000000001## Area conversion formula

### Metric system

$1 km^2 = 10^2 ha = 10^4 a = 10^6 m^2$

$1 m^2 = 10^4 cm^2 = 10^6 mm^2$

### United States customary units / Imperial units

$1 sq \ mi = 640 ac$

$1 ac = 4 ro = 4840 sq \ yd$

$1 sq \ yd = 9 sq \ ft$

$1 sq \ ft = 144 sq \ in = 929.0304 cm^2$

$1 sq \ in = 645.16 mm^2$

### Japanese units of measurement

$1\text{町} = 10\text{反} = 100\text{畝} = 3000\text{坪}$

$1\text{坪} = {\dfrac {400}{121}} m^2 \approx 3.305785 m^2$

$1\text{坪} = 10\text{合} = 100\text{勺}$

$1\text{畳／帖} = 1.62 m^2 \ (*)$

*** About tatami mats (畳 / 帖 / jō)**

When written as “畳”, it is not always 1.62 m^{2}. There are various dimensions of tatami mats such as Edo-ma and Kyo-ma. I made ”Unit Converter: Tatami”, so please use it.

When written as “帖”, it is 1.62 m^{2}. The “畳 / 帖” written in the recent housing advertisement is 1.62 m^{2}.