What ⅉ means
It denotes the imaginary unit in formulas that use this convention.
The imaginary unit is the quantity whose square is 1. This form distinguishes a mathematical quantity from an ordinary variable; the rest of the formula tells you how the author uses it.
Why is ⅉ a double-struck italic j?
The style marks a special mathematical quantity.
In 2002, a Unicode discussion described this small group of letterforms as matching existing publishing practice. The thread began with a request for a double-struck italic E for a formula.
Part of the collection
Don't confuse it with
3
Related characters
5
Questions people ask
1Why does ⅉ 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.
More like this
10
How to type or find ⅉ
- Search it as
- math j symbol · imaginary unit · double-struck italic j · UnicodeMath input
- Shows up in
- Anything that takes text · its shape is whatever your font draws
ⅉ\2149Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.