How to Say "I Don't Know" in Spanish

Quick Answer

I don’t know = no or no conozco

No Sé vs. No Conozco

The phrases no sé and no conozco come from the two verbs in Spanish used to express the idea of knowing: saberand conocer. It's important to know the differences between the two because they're not interchangeable.

No Sé

No sé is used to express a lack of knowledge or ability.

For example:

¿Pablo va a la fiesta? - No sé.
Is Pablo going to the party? - I don’t know.
No sé la respuesta.
I don’t know the answer.
No sé si quiero una limonada o un refresco.
I don’t know if I want a lemonade or a soda.
No sé hablar francés.
I don’t know how to (/ I can't) speak French.

No Conozco

No conozco is used to express a lack of familiarity with a person, place, or thing. Unlike no sé, it cannot be used as a stand-alone phrase.

For example:

No conozco a tu hermano.
I don’t know your brother.
No conozco esa película.
I don’t know that movie.

Click here to learn more about the differences between saber and conocer.

No Lo Sé

The pronoun lois often added to refer to something previously mentioned in a conversation.

For example:

Ya te dije que no lo sé.
I already told you I don’t know.

Alternatives to No Sé

No sé is by far the most common way to express your lack of knowledge in Spanish, though there are other ways. Check out the following table for more options!

Yo qué sé.
I don’t know.
Ni idea./ No tengo ni idea.No idea. / I have no idea.
No tengo ninguna idea.
I have no clue / idea.
¿Quién sabe?
Who knows?