¿Cuántas quieres?

Because cuántas agrees with a feminine plural noun that is understood from context.

Spanish changes cuánto depending on the gender and number of the thing being counted:

• cuánto = masculine singular
• cuánta = feminine singular
• cuántos = masculine plural
• cuántas = feminine plural

So ¿Cuántas quieres? means the speaker is asking about more than one feminine thing.

Example:

• ¿Cuántas galletas quieres? = How many cookies do you want?

Usually, an understood noun is being left out because it is already clear from the situation.

For example, if you are talking about:

• galletas → ¿Cuántas quieres?
• cervezas → ¿Cuántas quieres?
• camisas → ¿Cuántas quieres?

In English, we also sometimes do this:

• How many do you want?

So the full idea is often something like:

• ¿Cuántas [galletas] quieres?

Quieres is the tú form of the verb querer, which usually means to want.

So:

• yo quiero = I want
• tú quieres = you want
• él/ella quiere = he/she wants

In this sentence, quieres means you want.

Because Spanish often leaves out subject pronouns when they are not needed.

The verb ending already tells you who the subject is:

• quiero = I want
• quieres = you want
• quiere = he/she/you formal wants

So ¿Cuántas quieres? already clearly means How many do you want?

You could say ¿Cuántas tú quieres?, but that sounds unnatural in normal Spanish. If you include tú, it is usually for emphasis:

• ¿Cuántas quieres tú? = How many do you want, specifically?

It is informal singular, because quieres is the tú form.

If you wanted the formal version, you would say:

• ¿Cuántas quiere? = How many do you want? (formal, one person)

In Spain, if speaking to more than one person informally:

• ¿Cuántas queréis?

Formal plural:

• ¿Cuántas quieren?

Because cuántas is an interrogative word here.

Spanish adds a written accent to words like:

• qué
• cuál
• cuánto / cuánta / cuántos / cuántas
• cómo
• dónde
• cuándo

when they are used in questions or exclamations.

So:

• ¿Cuántas quieres? = question → accent needed

Compare with a non-interrogative use:

• Cuantas más, mejor is not standard with the same interrogative meaning; in normal questioning use, the accent is required.

Spanish uses both an opening question mark and a closing question mark:

• ¿ ... ?

So:

• ¿Cuántas quieres?

This is standard Spanish punctuation. The opening mark shows from the beginning that the sentence is a question.

In Spanish, question words like qué, cuándo, dónde, and cuántas normally come at the beginning of the question.

So the natural order is:

• ¿Cuántas quieres?

Putting quieres first would sound wrong in normal Spanish.

A very literal breakdown is:

• Cuántas = how many
• quieres = you want

Yes. That is grammatically correct, but it adds emphasis to tú.

• ¿Cuántas quieres? = neutral, normal
• ¿Cuántas quieres tú? = How many do you want?

This might be used if:

• you are comparing different people’s choices
• you want to stress that you are asking one specific person

Yes, very naturally.

Spanish often leaves out information that is obvious from context. If both people already know what is being discussed, ¿Cuántas quieres? is completely normal.

For example:

• At a bakery, while pointing at pastries
• At a table, talking about cookies
• In a shop, discussing shirts

If the context is not clear, you would usually include the noun:

• ¿Cuántas galletas quieres?

A simple Spain Spanish pronunciation guide would be:

• cuántas ≈ KWAN-tas
• quieres ≈ KYE-rehs

Very roughly together:

• KWAN-tas KYE-rehs

A few helpful notes:

• quie- sounds like kye
• the r in quieres is a light Spanish r, not a strong English r
• in Spain, the final s is clearly pronounced

The masculine plural version would be:

• ¿Cuántos quieres?

That would refer to masculine plural nouns, for example:

• libros = books
• cafés = coffees
• bollos = buns/pastries

Examples:

• ¿Cuántos libros quieres?
• ¿Cuántos quieres?

Not usually. In this kind of everyday context, ¿Cuántas quieres? is perfectly normal and natural.

In English, want can sometimes sound a little direct, but in Spanish querer is extremely common in everyday questions like this.

If you want to sound softer or more polite, other options are possible depending on context, for example:

• ¿Cuántas te pongo? = How many shall I give you? / How many would you like?
• ¿Cuántas vas a querer? = How many are you going to want?

But ¿Cuántas quieres? is completely standard.