Type one number and every unit of that kind comes out at once.
The Japanese traditional units are here too — tsubo, tatami, shaku, gō, shō, monme — and
each row says whether its value is exact by definition or only an approximation.
This page makes no network requests at all.
Every conversion is computed inside your browser. Once the page has loaded it keeps working in airplane mode.
(Currency is deliberately absent: exchange rates would need the network, which this page will not do.)
One tatami mat is not one fixed size — it varies by region and by building. Which one to use:
The “advertising standard” is the floor set by the Japanese real-estate advertising rules
(one mat must be shown as 1.62 m² or more). The others are computed from real mat sizes:
Kyōma 0.955×1.91 m, Chūkyōma 0.91×1.82 m, Edoma 0.88×1.76 m, Danchima 0.85×1.70 m.
Value
Unit
Basis and caveats
How this table is built (what the numbers are trusted from)
exact means a treaty, a law or a standard fixes the conversion at that value exactly. The only error is the rounding you asked for; the value itself carries no uncertainty. (1 inch = 2.54 cm, 1 shaku = 10/33 m, 1 monme = 3.75 g.)
approx. means the value depends on conditions, or does not divide evenly. Read the note before trusting it. (Mach changes with air temperature, a month is not a fixed length, a tatami mat differs by region.)
Every conversion goes through two steps: into the base unit, then out to the target unit. Each category names its base unit at the top.
Temperature is the exception: it carries an offset rather than a plain factor, so it uses its own formulas. Fuel economy (km/L against L/100km) is inverse rather than proportional.