Square KM

It means kilometres; “square” describes its one-cell layout. ㎞ is a length unit; ㎢ is square kilometres, an area.

This fullwidth km form comes from East Asian fixed-grid typography, where two Latin letters could occupy one ideograph-width character cell. Japanese typography calls that width 全角 (zenkaku, “fullwidth”). A 1992 edition of Korea’s KS X 1001 lists km among unit symbols; Japan’s JIS X 0213:2000 labels this form 全角KM.

Unicode keeps it as a compatibility character for exchanging text with older East Asian character sets.

When should I use ㎞ instead of km?

Use ㎞ when the unit needs one cell, especially in vertical text. A Japanese ebook-production guide recommends this form for vertical text, where separate k and m would occupy separate positions.

A text-normalization step called NFKC changes ㎞ to km, dropping the one-cell distinction. Japan’s e-Gov application help page lists it among unit symbols rejected by basic form fields as machine-dependent, as of 2026; use km when a field is strict.