Today I learned that the character for “jo” is “畳” (also the character for “tatami”) when used to measure room areas that are Japanese-style. For western-style rooms, the “帖” character is used but the pronunciation is the same. One jo is around 1.62m2 – 1.65m2 depending on where in Japan you happen to be, but the modern standard is 1.653m2, derived from the Nagoya tatami.
“Tsubo” (“坪”) is used to measure the area of an entire home (or to measure plots of land). One tsubo is equal to two tatami mats, or around 3.30579m2.
And here I thought imperial units were arbitrary…