Learn Russian: Сколько волонтёров вам нужно?

After quantity words like сколько (how many), много (many), and мало (few), Russian requires the genitive case. Since volunteers are countable, we use the genitive plural. For masculine nouns ending in a hard consonant like волонтёр, you form this by adding the ending -ов.

Why does the sentence use вам (to you) instead of вы (you)?

In Russian, you don't say 'You need X' with a normal subject and verb. Instead, you use an impersonal structure that literally translates to 'X is necessary to you'. The person experiencing the need must be in the dative case. Вам is the dative form of вы.

Since 'volunteers' is plural, why do we use the neuter singular нужно instead of the plural нужны?

This is a very common trap! Normally, if you need plural items, you do use the plural нужны (for example: Вам нужны волонтёры - You need volunteers). However, when you add a quantity word like сколько, that word takes over as the grammatical focus. These quantity words always trigger default neuter singular agreement, so you must use нужно.

How would I answer this question by saying 'We need five volunteers'?