What ㎹ means
It means megavolt: one million volts. Capital M is the SI prefix mega; V stands for volt.
Square unit labels follow an East Asian layout convention: short Latin abbreviations fit the width of one Chinese, Japanese, or Korean character. The wider family includes forms from older Korean character-set standards. Unicode listed ㎹ in 1993; that dates its encoding, not the start of the one-cell convention.
Why does ㎹ become MV?
Compatibility normalization can turn it into MV. NFKC is a standard form for normalizing text; it expands this boxed symbol to plain letters and drops the square.
A font without this glyph may show a blank placeholder box. Plain MV is more reliable for search and data exchange when the one-cell styling does not matter.
Technical and archival; suited to layouts that allot each character one fixed cell.
㎹ vs ㎷: uppercase M means mega; lowercase m means milli.
Don't confuse it with
1Questions people ask
1Why does ㎹ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ㎹
㎹\33B9Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.