How to Say I Don't Know in Spanish

How to Say I Don’t Know in Spanish

One of the first survival phrases every Spanish learner needs is No sé (no seh) — “I don’t know.” It’s short, polite, and universal. Spanish also offers more emphatic and casual versions for when “I don’t know” needs a little extra color.

The Essential Phrase: No sé

No sé — pronounced no seh

Just two syllables. No is the negation, and sé is the first-person present of saber, the verb for knowing facts and information. The written accent on sé matters: it separates the verb (“I know”) from the unrelated word se.

To say “I don’t know it” about something specific, add the pronoun lo: No lo sé.

Copy the Phrase

The Spanish for I don’t know is No sé (no seh).

All the Ways to Say I Don’t Know in Spanish

Spanish	Pronunciation	Meaning / When to Use
No sé	no seh	I don’t know — universal
No lo sé	no lo seh	I don’t know it (specific)
No tengo idea	no TEN-go ee-DEH-ah	I have no idea
Ni idea	nee ee-DEH-ah	No idea (casual)
No tengo ni idea	no TEN-go nee ee-DEH-ah	I have no idea at all (emphatic)
¿Quién sabe?	kyen SAH-beh	Who knows?
No estoy seguro / segura	no es-TOY seh-GOO-ro / -ra	I’m not sure
Quizás	kee-SAS	Maybe / perhaps
No sabría decirte	no sah-BREE-ah deh-SEER-teh	I couldn’t say (polite)

Saber vs. Conocer: Two Verbs for “Know”

Spanish splits “to know” into two verbs, and “No sé” uses saber:

• Saber — to know facts, information, or how to do something. No sé la respuesta (I don’t know the answer).
• Conocer — to be familiar with people, places, or things. No conozco a María (I don’t know María).

So “I don’t know” as a general statement is always No sé, never “no conozco.”

Formal vs. Informal

No sé is register-neutral — appropriate with your boss or your best friend. To soften it politely, add a phrase:

• Polite: “Lo siento, no lo sé” (Sorry, I don’t know), “No sabría decirle” (I couldn’t say — usted form).
• Casual: “Ni idea,” “No sé, la verdad” (I dunno, honestly), “Y yo qué sé” (How should I know? — slightly impatient).

Pronunciation Tips

• sé = “seh,” a clean short “eh” — never the English “say.”
• Spanish vowels are pure: a = “ah,” e = “eh,” i = “ee,” o = “oh,” u = “oo.”
• The qu in quién and quizás is a hard “k” (the u is silent): kyen, kee-SAS.
• Keep both words crisp and separate: “no” + “seh.”

Cultural Notes

Spanish speakers often pair a shrug with No sé or soften a flat “I don’t know” with No sé, pero… (I don’t know, but…) to keep the conversation going. The phrase ¿Quién sabe? (“who knows?”) carries a relaxed, philosophical shrug, while Y yo qué sé can sound a bit exasperated — handy to recognize, but use it carefully so you don’t seem dismissive.