¿Cuántos? ¿Cuántas?

You use ¿Cuántos? and ¿Cuántas? when you need to know how many of something there is.

How many students are there in this class?

How many hours do you study Spanish every night?

-feminine: ends in -as

It is used with feminine things/nouns:

How many girls are there?

How many flags are there?

¿Cuántas chicas hay?

¿Cuántas banderas hay?

¿Cuántas?

-masculine: ends in -os

It is used with masculine things/nouns:

How many boys are there?

How many books are there?

¿Cuántos chicos hay?

¿Cuántos libros hay?

¿Cuántos?

What's the difference between ¿Cuántos? and ¿Cuántas?

How many .... are there?

When asking about how many of something there are, you need to also include the word: there is/there are or when asking a question: are there/is there?

Use the word: hay