Unicode: Unit Symbols ㎜ ㎝ ㎡ ㎥ ㎐
Font:
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.