What 𝕛 means
Enter 1D55B, then press AltX. Word inserts 𝕛 from that hexadecimal Unicode value.
What does 𝕛 mean in math?
It is a mathematical j in a distinct letter style. As of 2026, no universal convention assigns lowercase 𝕛 one standalone meaning; the surrounding formula defines its role. Mathematical letter styles can carry different meanings, so double-struck j may denote something different from plain or italic j.
The blackboard-bold style grew from writing bold letters on blackboards by doubling some strokes, making them easier to distinguish from plain letters. Typewriters used the same double-striking trick when they lacked bold type; the style entered printed mathematics by the mid-1960s. Familiar double-struck capitals such as ℝ and ℂ name the real and complex numbers; lowercase letters belong to the same mathematical alphabet.
For mathematical notation: double-struck marks a distinct symbol, not general text emphasis.
NFKC or NFKD can turn 𝕛 into plain j, erasing the distinction. Avoid them on formulas.
Part of the collection
Don't confuse it with
1Related characters
3
More like this
11
How to type or find 𝕛
- Search it as
- mathbb j · blackboard bold j · double-struck j · outline j · hollow j · fancy j
- Shows up in
- Anything that takes text · its shape is whatever your font draws
𝕛\1D55B\mathbb{j} needs a font with lowercase double-struck glyphs.Why is 𝕛 a box on my screen?
fsymbols draws rare signs with its own fonts, so they show here even where your device has none. An app or website without such a font shows an empty box (□) or a question mark instead. Turn our fonts off to see each sign as your device draws it by itself: a box here means a box in your chats and documents too.
Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.