Unicode: Unit Symbols ㎜ ㎝ ㎡ ㎥ ㎐
length
㎚ ㎛ ㎜ ㎝ ㎞ ㏌
㎚ ㎛ ㎜ ㎝ ㎞ ㏌
area
㎟ ㎠ ㎡ ㎢
㎟ ㎠ ㎡ ㎢
volume
㎣ ㎤ ㎥ ㎦
㎣ ㎤ ㎥ ㎦
liquid volume
㎕ ㎖ ㎗ ㎘ ㏄
㎕ ㎖ ㎗ ㎘ ㏄
time
㎰ ㎱ ㎲ ㎳
㎰ ㎱ ㎲ ㎳
weight
㎍ ㎎ ㎏
㎍ ㎎ ㎏
bytes
㎅ ㎆ ㏔ ㎇
㎅ ㎆ ㏔ ㎇
hertz
㎐ ㎑ ㎒ ㎓ ㎔
㎐ ㎑ ㎒ ㎓ ㎔
voltage
㎴ ㎵ ㎶ ㎷ ㎸ ㎹
㎴ ㎵ ㎶ ㎷ ㎸ ㎹
watts
㎺ ㎻ ㎼ ㎽ ㎾ ㎿
㎺ ㎻ ㎼ ㎽ ㎾ ㎿
ohm
㏀ ㏁
㏀ ㏁
ampere
㎀ ㎁ ㎂ ㎃ ㎄
㎀ ㎁ ㎂ ㎃ ㎄
㎧
㎨
㎭
㎮
㎯
pascal
㎩ ㎪ ㎫ ㎬
㎩ ㎪ ㎫ ㎬
calorie
㎈ ㎉
㎈ ㎉
㍷
㍸
㍹
㏕
㎙
㍳
㏈
logarithm
㏑ ㏒
㏑ ㏒
time
㏂ ㏘ ㏙
㏂ ㏘ ㏙
㍱
㍲
㍴
㍵
㍶
㍺
㎊
㎋
㎌
㏃
㏅
㏆
㏇
㏉
㏊
㏋
㏍
㏎
㏏
㏐
㏓
㏖
㏗
㏚
㏛
㏜
㏝
㏞
㏟
㏿
Notes
Most of these are used in Japanese, as Japanese printing frequently use the style of putting things into a square box.
Unicode does not necessarily specify the meaning of a glyph/char it provides, because, some glyph can mean multiple things. For example, ㎰ (U+33B0: SQUARE PS) can mean “pico seconds”, or it can mean “postscript”.
Avoid using these. Because it's not a complete system for specifying units. For example, they don't cover all the metric system prefix.