Breakdown of Сколько масла ты покупаешь?
ты
you (singular)
покупать
to buy
сколько
how much / how long / as much / as many as
масло
butter
Questions & Answers about Сколько масла ты покупаешь?
Why does the word for butter end with an "а" here (масла instead of масло)?
This is the main rule for words of quantity! After сколько (how much / how many), the noun that follows must be in the Genitive case. For neuter nouns ending in -о like масло, the Genitive singular ending is -а, which gives us масла.
Is сколько used for both "how much" and "how many"?
Yes! In Russian, сколько covers both. Here, because butter is uncountable, it translates to "how much". If you used it with something countable, it would mean "how many". In both cases, the noun following it takes the Genitive case.
Does масло mean "butter" or "oil"?
It means both! Масло is the general word for fat used in cooking (and even motor oil). Depending on the context, it could mean butter, vegetable oil, or olive oil. We translated it as "butter" here, but "How much oil are you buying?" is just as correct.
Why is the verb покупаешь used here instead of покупаете?
The verb must match the subject. Here, the subject is the informal "you" (ты), so the verb takes the -ешь ending. If you were asking someone formally, or asking a group of people, you would use вы and the verb would change to покупаете: Сколько масла вы покупаете?