How to Say I Don’t Know in Spanish: 6 Must Know Phrases

If you’re learning Spanish, at some point, you may need to say that you don’t know something. Since knowing how to do this will allow them to express their doubts faster, many people wonder how to say ‘I don’t know’ in Spanish.

Depending on the situation, there are some common expression that speakers use to say ‘I don’t know’ in Spanish:

  • No sé – I don’t know
  • ¡Sepa! – Who knows / I don’t know
  • Ni idea / No tengo idea – No idea / I have no idea
  • ¡Quién sabe! – Who knows
  • ¡Sabe! – I don’t know / Who knows
  • No lo conozco / No conozco – I don’t know it/him/her

In the following sections, we’ll explain to you when and how to use each one of these phrases. Additionally, we’ll provide you with phrase structures and examples of how to apply these expressions in real-life situations.

By the end of this, you’ll have different options to say ‘I don’t know’ in Spanish.

1. No sé / No lo sé – I don’t know

No sé or no lo sé are the direct translation of ‘I don’t know’. As a result, this is one of the most common ways to express that you don’t know something in Spanish. As a standard term, ‘no sé’ can be used in all Spanish speaking countries in both formal and casual situations.

This expression can be used alone as a response to someone’s question or you can use it as a way to express that you don’t know something.

Tú: ¿Cómo está Paula?You: How is Paula?
Tu amigo: La verdad no sé, no la he visto. Your friend: To be honest I don’t know, I haven’t seen her. 
Tú: ¿Estudiaste para el examen?You: Did you study for the test?
Tu amigo: ¿Es hoy? No sabía, pensé que era hasta la próxima semana.Your friend: Is it today? I didn’t know, I thought it wouldn’t be until next week. 

Additionally, you can use no sé to mention the thing or subject that you don’t know. Notice that you can conjugate the verb to match any tense you may need:

No + [ saber conjugated] + que + [info]

No supe que teníamos que venir de blanco.
I didn’t know that we needed to wear white.

Maestra, no sabíamos que el examen era hoy.
Prof, we didn’t know that the exam was today.

Lana, ya te dije que no sé donde están tus llaves.
Lana, I already told you that I don’t know where your keys are.

Take Note: No lo sé is a variation of ‘no sé’. It can be translated as ‘I don’t know’ or ‘I don’t know it’. Even though they can be used as synonyms, ‘no sé’ is slightly more common than ‘no lo sé’. 

2. ¡Sepa! – Who knows

If you want to learn more casual expressions to say ‘I don’t know’ in Spanish, ¡sepa! may be one of your best options. ‘¡Sepa!’ is closer in meaning to the expressions ‘who knows’ and ‘I don’t know’.

This expression doesn’t need to be conjugated and you can use it as a way to respond to someone’s questions or to introduce the thing or subject that you don’t know. Here are some examples:

Tu mamá: ¿Qué quería tu hermana?Your mom: What did your sister want?
Tú: ¡Sepa! No me dijo.You: I don’t know! She didn’t tell me. 
Tu amigo: ¿Cómo está Lucía? Hace mucho que no viene.Your friend: How is Lucia? She hasn’t visited for a while.
Tú: ¡Sepa! Le he mandado mensajes, pero no me contesta. You: Who knows. I have texted her, but she doesn’t answer.  

If instead of answering to a previous statement you want to create a sentence that mentions the thing or subject you don’t know, you need to follow this structure: 

Sepa + [questioning word] + [info] 

Sepa quién es esa señora.
I don’t know who that lady is.

¿No encontraste tus llaves? Sepa dónde estarán.
You didn’t find your keys? Who knows where they are.

Ben vino hace rato, pero sepa qué quería.
Ben came a while ago, but who knows what he wanted.


  • Sepa la bola. ‘Who knows’ or ‘I don’t know’. This expression is only applicable in Mexico. 

3. Ni idea / No tengo idea – No idea

Both ‘ni idea’ and ‘no tengo idea’ are polite and standard expressions that we use to express that we don’t know something in Spanish. These phrases can be translated as ‘no idea’ or ‘I have no idea’. 

Even though it’s not a rule of thumb, ‘ni idea’ tends to be more commonly used as a way to respond to someone’s statement or answer their question. On the other hand, ‘no tengo idea’ can be used both as a response or as a way to mention the things you don’t know. 

[No tengo idea] + de + [questioning word] + [information]

No tengo idea de quién es Alicia.
I have no idea who Alicia is.

¡Déjame en paz! No tengo idea de qué estás hablando.
Leave me alone! I have no idea what you’re talking about.

Tú: ¿Sabes cómo arreglar esto?You: Do you know how to fix this?
Tu amigo: Ni idea, la neta. Your friend: To be honest, I have no idea.
Tu amigo: ¿Cuánto costará un boleto a México?Your friend: How much would a ticket to Mexico cost?
Tú: Ni idea, pregúntale a Billy, él fue el año pasado. You: No idea, ask Billy, he went last year. 

4. ¡Sabe! – I don’t know

Another popular way to say ‘I don’t know’ in conversational Spanish, it’s by using the word ¡sabe! This expression is very similar to ‘¡sepa!’, but it’s not as informal as this word. ‘¡Sabe!’ is usually applied to answer a question or statement that is being presented right now. It means ‘who knows’ or ‘I don’t know’.

Additionally, in some cases, it can also imply that the statement causes you some kind of surprise or confusion. 

Tú: Mamá, ¿has visto a mi hermano?You: Mom, have you seen my brother?
Tu mamá: Sabe dónde andará, no lo he visto hoy.Your mom: Who knows where he is, I haven’t seen him.  
Tú: ¿Por qué no vino Luisa, Javier?You: Why didn’t Luisa come, Javier?
Tu amigo: ¿No vino? ¡Sabe! No he hablado con ella.Your friend: She didn’t come? Who knows, I haven’t talked to her.
Tú: ¿Qué pasó ayer en el centro?You: What happened yesterday in downtown?
Tu amigo: ¡Sabe! Pero había muchos policías y ambulancias.Your friend: I don’t know, but there were a lot of cops and ambulances.  

5. ¡Quién sabe! – Who knows

Quién sabe is another common way to say ‘I don’t know’ in Spanish. Even though it’s a standard expression, ‘quién sabe’ tends to be more popular in casual conversations. Additionally, this phrase is used to express that you don’t know something or to answer someone’s questions.

[Quién sabe] + [questioning word] + [info]

¡Quién sabe qué pasó en la casa de la vecina!
Who knows what happened in the neighbor’s house!

No he visto tu cartera, quién sabe dónde la habrás dejado.
I haven’t seen your wallet, who knows where you left it.

Tú: ¿A qué hora crees que se termine esto?You: What time do you think this is going to finish?
Tu amigo: ¡Quién sabe! Pero ya me quiero ir.Your friend: Who knows! But I want to go.

Take Note: Something to keep in mind when using this expression is that, in other contexts, quién sabe can be used to ask if someone knows something. However, in that situation, ‘quién sabe’ would always be used as a question and it would have further information. 

6. No lo conozco / No conozco – I don’t know it/him/her

In Spanish, no conozco and no lo conozco can be translated as ‘I don’t know’ or ‘I don’t know it’. But even though they share the same translation, these expressions convey that someone doesn’t know another person, object or place.

‘No lo conozco’ is used for the same purpose. However, because it works with the direct object pronoun lo, you need to make sure people know what you’re referring to.

No [conocer conjugated] + a + [person] 

Lo siento, no conozco a tu prima, ¿quién es?
I’m sorry, I don’t know your cousin, who is she?

Nosotros no conocemos muy bien a nuestro jefe.
We don’t know our boss very well.

No [conocer conjugated] + [place] 

Todavía no conozco México.
I am not familiar with Mexico yet.

No conocemos tu casa porque nunca nos has invitado.
We don’t know your house because you’ve never invited us.

Tú: ¿Quién es el novio de Claire?You: Who is Clair’s boyfriend?
Tu amigo: Todavía no lo conozco.Your friend: I haven’t met him yet

Take Note: Because they both mean ‘to know’, understanding when to use saber or conocer is not always clear for people learning Spanish. Check this guide to learn the difference between conocer and saber.

Wrapping Up

Knowing how to say I don’t know in Spanish not only will allow you to express your doubts, but it will also allow you to express that you’re in the dark about a certain topic or situation. Because of that, in this article, we’ve reviewed different expressions that you can use to say ‘I don’t know’.

Additionally, we provided you with the most appropriate contexts to apply these expressions as well as some examples that you can use as guidance.

Daniela Sanchez

¡Hola! Soy Daniela Sanchez, I've been studying Spanish professionally as well as teaching it in Mexico and online for over 10 years. I’ve taught Spanish to a wide array of foreigners from many backgrounds. Over the years, I've made it my mission to work hard on refining many challenging to understand grammar topics to make my students' learning experiences easier, faster and more enjoyable. Read More About Me

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