6 Easy Ways to Say I don’t know in Spanish


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

Even though all these expressions are very common ways to say ‘I don’t know’ in Spanish, some of them may be more suitable for certain situations than others. As a result, 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 – I don’t know 

In Spanish, no sé is the direct translation of ‘I don’t know’. As a result, this is one of the most common and standard 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. 

SpanishEnglish
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. 
SpanishEnglish
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. In this context, ‘¡sepa!’ is a Spanish word that we use to say ‘I don’t know’ in casual conversations. As a result, it’s closer in meaning to the expressions ‘who knows’ and ‘I don’t know’. 

As an expression, ‘¡sepa!’ 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:

SpanishEnglish
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. 
SpanishEnglish
Tu amigo: ¿Cómo está Lucía? Hace mucho que no vieneYour 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 here they are

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

Variation: 

  • 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

SpanishEnglish
Tú: ¿Sabes cómo arreglar esto?You: Do you know how to fix this?
Tu amigo: Ni idea, la neta. Your friend: To be honest, no idea.
SpanishEnglish
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!

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. 

This phrase can be translated as ‘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. 

SpanishEnglish
Tú: Mamá, ¿has visto a mi hermano?You: Mom, have you seen my brother?
Tu mamá: Sabe dónde andará, no le he visto hoy. Your mom: Who knows where he is, I haven’t seen him.  
SpanishEnglish
Tú: ¿Por qué no vino Luisa, Javier?You: Why didn’t Luisa come, Javier?
Tu amigo: ¿No vino? ¡Sabe! No he hablado con ellaYour friend: She didn’t come? Who knows, I haven’t talked to her.
SpanishEnglish
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 

SpanishEnglish
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

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 these phrases seem to be synonyms with the phrases we’ve learned so far, the truth is that, in Spanish, ‘no conozco’ and ‘no lo conozco’ are used for other purposes.

‘No conozco’ is used to express that a person doesn’t know another person, object or place. And ‘no lo conozco’ is used for the same purpose with the only difference that with this expression you need to mention the person, object or place you’re talking about.

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 porque siempre está de viaje
We don’t know our boss very well because he’s always traveling 

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 

SpanishEnglish
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

Related Resource: What’s the Difference Between Saber and Conocer

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.

Since these types of situations are very common in all languages, in this article, we compiled these different expressions that you can use to say ‘I don’t know’ in Spanish.

Additionally, we provided you with the most appropriate contexts to apply these expressions as well as some examples that you can use as guidance.Hopefully, now you have a better idea of how to say ‘I don’t know’ in Spanish.

Daniela Sanchez

¡Hola! Soy Daniela Sanchez, I’ve taught Spanish in Mexico to a wide array of foreigners. From students and tourists to doctors and soldiers who’ve moved and visited here over the years. During the day I’m a freelancer and marketer, while at night I’m here writing for students of the world wide web looking to learn Spanish. I hope you find what you’re looking here during your journey into Español 🙂 Read More About Me

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