The most common unknown abbreviation is unk., with a period in notes and running text, or UNK in all capitals on forms, logs and spreadsheets. A longer version, unkn., shows up now and then, but unk is the one most readers will recognize.
It fills a blank when the answer exists but nobody has it. A family tree with a great-grandmother's birth year missing, a police report without a license plate, a medical chart with an unclear allergy history: each might say unk instead of leaving the box empty.
Quick facts
Main abbreviation
unk. (lowercase, with period)In forms and data
UNK (capitals, no period)Less common
unkn.Single letter code
U, on some forms with a set list of choicesMeans
The answer exists but is not knownNot the same as
N/A, not applicable, or TBD, to be determinedPlural
No plural form; write unk. for each entry
Which unknown abbreviation to use
| Form | Where it fits | Example |
|---|---|---|
| unk. | Handwritten notes, family trees, reports | Born: unk. |
| UNK | Data fields, spreadsheets, coded forms | Vehicle color: UNK |
| unkn. | Older records, some catalogs | Maker: unkn. |
| U | Forms with single letter options | Answer: Y / N / U |
| ? | Quick personal notes only | Date: ? |
If a form gives you a list of codes, use the one it lists. Many databases treat UNK as a fixed value, so writing "unknown" or "?" in the box can cause an error or end up sorted wrong.
Unknown vs N/A vs TBD
People swap these freely on forms, yet each label tells the reader something distinct:
- Unknown (unk.): there is an answer, but you do not have it. "Father's middle name: unk."
- N/A, not applicable: the question does not apply to you. "Spouse's name: N/A" for someone who is not married.
- TBD, to be determined: the answer has not been decided yet. "Meeting room: TBD."
- TBA, to be announced: the answer is decided or coming, but not shared yet.
On a school emergency form: "Allergies: unk." This tells the nurse no one knows yet, which is very different from "Allergies: none," so she will follow up with the family.
Where you will see unk
- Genealogy: family records mark missing dates and places as unk.
- Police and incident reports: "Suspect height: UNK."
- Medical charts: history items no one can confirm.
- Inventory and shipping: a part with no maker listed.
- Science and survey data: a code for answers that are missing or unclear.
- Library and museum catalogs: an artist or author whose name is lost.
In book citations, a missing author is marked differently. Writers often use anon. for anonymous, and n.d. when no date is given, rather than unk.
Writing it correctly
In ordinary sentences, spell out unknown. It is a short word and the abbreviation looks like jargon in a letter or essay. Save unk for tight spaces: tables, labels, forms and notes.
- Use a period in lowercase: unk.
- Drop the period in capitals: UNK
- Do not add an s. Five missing entries are each marked unk.
Other short forms from forms and lists, such as misc. for miscellaneous and c. for circa, follow the same habits. Browse more in common abbreviations.
Unknown in sentences and notes
- "Cause of the delay: unk. Still checking with the carrier."
- "Grandfather's birthplace listed as unk. in the census copy."
- "Caller ID showed UNK, so the number was blocked."
- "Original price unk.; tag missing."
When you can, add a short note on why the answer is missing or who might know it. That makes the next person's search easier.
Questions people ask
What is the abbreviation for unknown?
The abbreviation for unknown is usually unk. In data and forms it is often written UNK in capitals.
Is unknown the same as N/A?
No. Unknown means an answer exists but you do not have it, while N/A means the question does not apply.
Does unk need a period?
In lowercase notes, write unk. with a period. In all capitals, as UNK in a data field, the period is left off.
What does UNK mean on a form?
UNK on a form means the information is unknown. It is a placeholder so the field is not left blank.
Can I use a question mark instead?
A question mark works in your own notes, but forms and databases usually expect UNK or a listed code. Use the code the form asks for.