Difference between "poco" and "un poco" in Spanish

In Spanish we use the word "poco" in different ways to express an indefinite quantity of something or to express infrequency but sometimes it is difficult to distinguish between "poco" and "un poco". 

For example:

Notice how in the first case, in English the literal translation doesn't work well, so it is generally translated as a negative sentence (not much). 

Let's see other examples:

You can emphasise the quantity by adding muy:

In all the examples above, poco and un poco accompany verbs, as adverbs they are invariable.

Let's see how they work as adjectives when accompanying nouns.

Poco/-a/-os/-as + nouns

As you can see in the examples above poco agrees in gender and number with the noun it accompanies (poco  alcohol, poca grasa, pocos amigos, pocas cervezas).

Poco (invariable) + adjectives

Poco can be an adverb accompanying adjectives, with the meaning: "not very..." 

Bear in mind that in this case poco is invariable, as shown on the examples above.

Un poco de + nouns in singular

Notice how we add "de" to express "a bit of something". Even when accompanying nouns, it is invariable in the singular, so it does not change to una poca de with feminine singular nouns.

 Unos pocos/unas pocas de + nouns in plural

See how with plural nouns we drop the "de".

When we use unos pocos/unas pocas + noun it has the same meaning as "algunos/algunas" (some).

See also:

• Using demasiado, bastante, suficiente, poco, tanto and mucho to express quantity in Spanish (quantitative adjectives)
• Using demasiado, bastante, suficiente, poco, tanto and mucho to express quantity in Spanish (quantitative pronouns)
• Using demasiado, bastante, un poco, mucho, tan, tanto and muy for too, quite, a bit, so, so much and very in Spanish (quantitative adverbs)