Learn Hardcore German: Wir kaufen zwei Liter Milch.

German typically expresses measure and content without a preposition: zwei Liter Milch, ein Glas Wasser, drei Flaschen Bier. You only use von when you need to make it definite/specific or contrastive, e.g. zwei Liter von der Milch (two liters of that particular milk we were talking about). The short form without von is by far the most common.

Why is there no article before Milch?

Mass nouns after a measure word usually appear without an article when the reference is indefinite: zwei Liter Milch, ein Kilo Reis. If you make it definite, you can add an article: zwei Liter der Milch (genitive) or colloquially zwei Liter von der Milch (with von + dative).

What case is the whole phrase zwei Liter Milch in?

It’s the direct object of kaufen, so the whole noun phrase is in the accusative. With no article, you can’t see case on the nouns here. A pronoun test shows it’s accusative: Wir kaufen sie (“We’re buying them/it”).

What case is Milch in within the phrase?

Grammatically it’s a “content/measure” complement often analyzed as a genitive attribute. If you make it explicit/definite, the genitive shows: zwei Liter der Milch (genitive singular of feminine die Milch). In the bare form (zwei Liter Milch) no article appears, so you don’t see genitive marking.

Why is it zwei Liter and not “zwei Liters”?

Many measurement units have an unchanged plural in German. The plural of der Liter is die Liter, so after numbers you say zwei Liter, fünf Liter, etc. This is normal for units like Liter, Meter, Gramm, Euro (see the dative note below).

Do I ever add -n to Liter?

Yes, in the dative plural you add -n: mit zwei Litern Milch, zu den fünf Litern. This is a general rule for many plural nouns in the dative.

Can I just say Wir kaufen Milch?

Yes. With mass nouns, a bare form without quantity is fine and means “some milk” in English: Wir kaufen Milch.

Is there a difference between kaufen, einkaufen, holen, and besorgen here?

kaufen = to buy (transitive): Wir kaufen zwei Liter Milch.
einkaufen = to do (the) shopping. Often intransitive: Wir kaufen ein. You will also hear it with objects in everyday speech: Wir kaufen Milch ein.
holen = to fetch/pick up: Wir holen Milch (go get it and bring it).
besorgen = to get/procure (stresses managing to obtain): Wir besorgen Milch.

Does German present tense here also cover the near future (“We’re going to buy”)?

Yes. Wir kaufen zwei Liter Milch can mean a present arrangement/plan, just like English “We’re buying/We’re going to buy two liters of milk.”

How do I ask “How much milk are we buying?” and “How many liters are we buying?”

Quantity of a mass noun: Wie viel Milch kaufen wir? — Zwei Liter.
Number of units: Wie viele Liter kaufen wir? — Zwei. Note: Standard spelling is wie viel (two words), though wieviel also occurs.

What are the genders of the nouns?

der Liter (masculine)
die Milch (feminine)

Why are Liter and Milch capitalized?

All nouns are capitalized in German, including unit names used as nouns: Liter, Meter, Milch, Wasser.

What’s the plural of Milch?

Normally, Milch is uncountable and has no plural. If you need a plural idea, you use something like Milchsorten (types of milk). A true plural Milche exists only in very technical/rare contexts.

How would I negate the sentence?

General negation: Wir kaufen keine Milch.
Negating the amount: Wir kaufen keine zwei Liter (Milch) = “not as much as two liters / not two liters.”

Can I add adjectives, and how do they agree? Is it zwei Liter kalte Milch or zwei Liter kalter Milch?

Both occur:

Everyday/useful: zwei Liter kalte Milch (treats “kalte Milch” as a description of the content).
More formal/grammatical genitive-of-content: zwei Liter kalter Milch (adjective shows strong genitive feminine -er). In practice, the first version is very common and perfectly acceptable, especially in recipes and speech.

Are there word-order variants?

Yes:

Statement with focus shift: Zwei Liter Milch kaufen wir.
Yes/no question: Kaufen wir zwei Liter Milch?
Wh-question: Wie viel Milch kaufen wir? / Wie viele Liter kaufen wir?

How would I refer back to the whole object with a pronoun?

Feminine mass noun focus: Wir kaufen Milch. Wir kaufen sie.
Neutral idea/amount: Wir kaufen das.
For just the unit (if previously mentioned): Wir kaufen zwei.

Any pronunciation tips?

Wir: initial “w” is like English “v” [viːɐ̯].
kaufen: “au” = [aʊ̯], stress on the first syllable: [ˈkaʊ̯fən].
Liter: long “i” [ˈliːtɐ].
Milch: final “ch” is the soft ich-sound

Can I write the number as a digit? Any unit abbreviations I should know?

Yes: Wir kaufen 2 Liter Milch. Abbreviation: l or L (both used; capital L helps avoid confusion with the digit 1): 2 l Milch or 2 L Milch. Decimals use a comma in German: 2,5 Liter; you can also say zweieinhalb Liter.

How does this pattern work with other containers/units?

Same structure:

zwei Flaschen Milch
ein Kilo Äpfel / ein Kilogramm Äpfel (often unchanged plural after numbers: zwei Kilo Äpfel; colloquial zwei Kilos also occurs)
drei Meter Stoff The content noun is usually bare unless made definite: zwei Flaschen des Weins (formal) or zwei Flaschen von dem Wein (colloquial/definite).