How to say “I don't know” in Spanish

No sé

Pronunciation: noh SEH · Syllables: no SÉ

The most common way to say "I don't know" in Spanish is "No sé" (pronounced noh SEH). It is neutral and works in almost any situation, with friends, strangers, at work or in a shop. You can also say "No lo sé" (I don't know it) or, more casually, "Ni idea" (No idea).

How to pronounce “No sé”

Say the Spanish 'o' in 'no' short and pure, without gliding into an 'oo' sound like English 'no-w'.
The 'é' in 'sé' sounds like the 'e' in 'bet', not like 'say', so keep it short with no 'ee' at the end.
Put the stress on 'sé' and make the 's' a clean, crisp hiss, never a 'z' or 'sh' sound.

What it literally means

"No sé" is literally "not I-know." "Sé" is the irregular yo-form of the verb saber (to know), which comes from Latin sapere, meaning 'to taste, to be wise.' The accent on "sé" separates it from the pronoun "se." Spanish usually drops the subject "yo" because the verb ending already shows who is speaking.

How to say “I don't know” in Spanish: No sé — casual to formal, by country, replies and common mistakes — Cheat sheet — tap to enlarge

Other ways to say it, from casual to formal

Ni ideaNo idea · casual chats with friends and familyVery casual
No tengo ideaI have no idea · everyday conversation, a bit more emphaticCasual
No tengo ni ideaI have absolutely no idea · stressing that you really don't knowCasual
¿Quién sabe?Who knows? · talking about the future or something nobody can knowCasual
No lo séI don't know (it) · answering a specific question, slightly fuller and more carefulNeutral
No estoy seguro / seguraI'm not sure · you have a guess but aren't certainNeutral
No sabría decirleI couldn't tell you · polite answer to a customer, boss or stranger (usted)Formal
Lo desconozcoI'm not aware of that · formal writing, offices, official contextsFormal

By country

SepaMexico · Very common casual shrug-word, short for 'quién sabe'. Often said as 'Sepa la bola' for a playful 'who knows'.
Qué sé yoArgentina / Uruguay · Used constantly as 'I dunno' and also as a filler like 'I mean, whatever' in the middle of sentences.
No cachoChile · From the slang verb 'cachar' (to get, to understand). It means 'I don't get it' or 'no clue.' Very casual.
Yo qué séSpain · Very frequent casual 'how should I know?'. Depending on tone, it can sound a little impatient.

In text messages

ns = dunno (short for 'no sé')nose = dunno ('no sé' typed fast with no space or accent; it also happens to spell the word for 'nose')ns q hacer = dunno what to do

Example sentences

—¿Dónde está Ana? —No sé."Where's Ana?" "I don't know."
No sé qué hora es.I don't know what time it is.
Lo siento, no sé dónde está la estación.Sorry, I don't know where the station is.
No sé si voy a ir a la fiesta.I don't know if I'm going to go to the party.
Ni idea, pregúntale a tu hermano.No idea, ask your brother.
La verdad, no sabría decirle cuánto cuesta, pero puedo preguntar.Honestly, I couldn't tell you how much it costs, but I can ask.

Mini dialogue: Asking for directions on the street

Disculpe, ¿sabe dónde hay una farmacia por aquí?

Excuse me, do you know where there's a pharmacy around here?

Ay, lo siento, no sé. No soy de aquí.

Oh, I'm sorry, I don't know. I'm not from here.

No se preocupe. ¿Y sabe si hay un supermercado cerca?

Don't worry. And do you know if there's a supermarket nearby?

Creo que hay uno en la esquina, pero no estoy segura.

I think there's one on the corner, but I'm not sure.

Muchas gracias, voy a ver.

Thanks a lot, I'll go check.

How to reply

No te preocupes.Don't worry (informal).
No pasa nada, gracias igual.No problem, thanks anyway.
Bueno, voy a preguntar a otra persona.Okay, I'll ask someone else.
Yo tampoco.Me neither.

Grammar: Saber: 'sé' + question word

Saber (to know facts or information) is irregular in the yo form: 'sé', not 'sabo'. To say what you don't know, add a question word right after it (qué, dónde, cuándo, cómo, quién) or 'si' (if). These question words keep their accent. Use conocer, not saber, for people and places you aren't familiar with.

No sé cómo se dice en español.I don't know how to say it in Spanish.
No sé si tienen mesa libre.I don't know if they have a free table.

Common mistakes

✗ ~~Yo no sabo.~~✓ Yo no sé.

Saber is irregular in the yo form, so the correct word is 'sé'.

✗ ~~No conozco dónde está el baño.~~✓ No sé dónde está el baño.

Use saber for facts and information, and conocer for people and places you're familiar with.

✗ ~~No se.~~✓ No sé.

Without the accent, 'se' is a pronoun; 'sé' with the accent means 'I know'.

Culture tip

Native speakers say "No sé" all the time, often with a shrug, raised eyebrows or a downturned mouth, and sometimes stretch it out as "No sééé" when they are unsure. With strangers, it sounds friendlier to soften it with "Lo siento, no sé" or "La verdad, no sé." A plain "Ni idea" can feel a bit abrupt in formal situations. In customer service, staff often say "No sabría decirle" and offer to find out.

Questions people ask

What's the difference between "No sé" and "No lo sé"?

Both mean "I don't know" and are interchangeable in most situations. "No lo sé" (literally "I don't know it") sounds a bit fuller and more deliberate, while "No sé" is quicker and more common in everyday speech.

Does "sé" need an accent mark?

Yes. "Sé" with an accent means "I know" (from saber). "Se" without it is a pronoun, as in "se llama". In casual texting people often skip it, but in correct writing you need it.

How do I say "I don't know" formally in Spanish?

"No lo sé" is already polite. For extra courtesy, say "Lo siento, no sabría decirle" (Sorry, I couldn't tell you). In formal writing, "Lo desconozco" is also used.

Is "Ni idea" rude?

It isn't rude, but it is casual and can sound dismissive with strangers or in formal settings. Use it with friends and family, and say "No sé" or "No tengo idea" elsewhere.