Sofia · Learn Spanish How to say it in Spanish How to Say I Don't Know in Spanish (No Sé)
I don’t know in Spanish is no sé — two tiny words that carry a surprising amount of grammar. That accent on sé isn’t decoration: it’s the difference between “I know” (the verb) and se (a reflexive pronoun). Say it right and you sound natural; miss it and you’re technically saying something else. Beyond the basics, Mexican Spanish has some of the most charming ways in the language to shrug — quién sabe, ni idea, sepa.
The main way to say it
No sé — pronounced noh SEH.
The pronunciation details that matter:
- Sé is one clean syllable, stressed, with a clear “eh” vowel: SEH, not “say.” No diphthong glide at the end.
- The accent mark on sé marks it as the verb saber (“to know [facts]”), first person: yo sé = “I know.” No sé = “I don’t know.”
- Say it as two even beats: noh — SEH. Don’t swallow the no.
The key distinction English hides: Spanish has two verbs for “to know.”
- Saber = to know information, facts, how to do something. No sé la respuesta (“I don’t know the answer”), no sé nadar (“I don’t know how to swim”).
- Conocer = to know a person or place (be familiar with). No conozco a María (“I don’t know María”), no conozco esa ciudad (“I don’t know that city”).
So “I don’t know” as in “I lack that fact” is almost always no sé (saber). If someone asks whether you know a person, you’d say no lo/la conozco.
Variations
| Phrase | Meaning | Register |
|---|---|---|
| No sé | I don’t know | Universal |
| No lo sé | I don’t know (it) | Universal, slightly fuller |
| No tengo idea | I have no idea | Universal, emphatic |
| Ni idea | No clue | Casual |
| No tengo ni idea | I have no clue at all | Casual, emphatic |
| Quién sabe | Who knows | Casual, very Mexican |
| Sepa | Beats me / who knows | Very casual, Mexican slang |
| Sepa la bola | Beats me (nobody knows) | Casual, playful, Mexican |
| No estoy seguro / segura | I’m not sure | Softer, polite |
The famous Mexican shrug is quién sabe — literally “who knows,” delivered with a little lift of the shoulders. Even more colloquial is sepa (or the fuller sepa la bola), a fixed slang expression meaning “who could possibly know.” It’s affectionate and very local; use it with friends, not in a job interview.
When you want to be gentle rather than blunt, no estoy seguro (“I’m not sure”) softens the “no sé” and buys you room.
Hear it in context
Answering a question you genuinely can’t (casual):
— ¿A qué hora abre el museo? — Uf, no sé. Déjame checar en mi celular. — Va. Gracias. — Ni idea, la verdad, pero ahorita lo vemos.
What time does the museum open? — Ugh, I don’t know. Let me check on my phone. — Cool. Thanks. — No clue, honestly, but we’ll see in a sec.
Very Mexican shrug between friends:
— ¿Por qué canceló la fiesta? — Quién sabe. No dijo nada. — Qué raro, ¿no? — Sepa. Ya nos enteraremos.
Why did she cancel the party? — Who knows. She didn’t say anything. — Weird, right? — Beats me. We’ll find out eventually.
Common mistakes
- Dropping the accent and saying “no se.” In writing that’s a different word. In speech, make sure you’re saying the verb sé (SEH), stressed, meaning “I know.”
- Using “no conozco” for facts. No conozco is for people and places, not information. “I don’t know the answer” is no sé la respuesta, never no conozco la respuesta.
- Translating “no idea” as “no idea.” Spanish needs the verb: no tengo idea or ni idea, not a bare no idea.
- Over-formalizing. In casual talk, natives just say no sé or quién sabe. A full no tengo conocimiento de eso sounds stiff and bureaucratic.
Mexico vs Spain notes
The plain answer, no sé, is universal — say it anywhere and you’re understood.
- Quién sabe is used across Latin America but is especially a Mexican reflex, often with the shoulder shrug.
- Sepa / sepa la bola is distinctly Mexican slang; a Spaniard would more likely say ni idea or the very Spanish no tengo ni pajolera idea (mild, informal emphasis).
- The pronunciation is essentially the same on both sides of the Atlantic; the s sound in sé doesn’t lisp in either place because it’s an s, not a c/z.
Related phrases
Not knowing usually leads straight into asking — pair these:
- How to say I don’t understand in Spanish — for when the problem is comprehension, not information.
- How to say what does that mean in Spanish — the natural follow-up when you’re lost.
- Round out your basics with our guide to common Spanish phrases.
FAQ
Why does “sé” have an accent? The accent distinguishes the verb sé (“I know”) from the pronoun se. Without the accent, se is a completely different word, so no sé needs it to mean “I don’t know.”
What’s the difference between “no sé” and “no conozco”? No sé (from saber) is for facts, information, and skills. No conozco (from conocer) is for people and places. “I don’t know the way” = no sé el camino; “I don’t know her” = no la conozco.
What does “quién sabe” mean? Literally “who knows” — a casual, very Mexican way to say “I don’t know / beats me,” usually with a shrug. It’s friendly and extremely common in everyday speech.
Is “sepa” rude? Not rude, just very informal slang. Sepa (or sepa la bola) means “who could know” and is best kept for friends and relaxed settings, not formal ones.
How do I say “I’m not sure” more politely? No estoy seguro (if you’re male) or no estoy segura (if you’re female). It’s softer than a flat no sé and useful when you want to hedge.