leer
empty
Not filled with anything; without contents.
Das Glas ist leer, könntest du mir bitte noch etwas Wasser einschenken?
The glass is empty; could you please pour me some more water?

empty
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empty
Not filled with anything; without contents.
Das Glas ist leer, könntest du mir bitte noch etwas Wasser einschenken?
The glass is empty; could you please pour me some more water?

The adjective 'leer' (empty) belongs to a word family. The corresponding noun is 'die Leere' (emptiness/the void), and the verb is 'leeren' (to empty something).
Er blickte in die Leere.
He stared into the void.
In the meaning 'ohne Inhalt' (without contents), 'leer' (empty) is often used for containers, rooms, or places. Typical combinations are 'eine leere Flasche' (an empty bottle), 'ein leeres Zimmer' (an empty room), or 'leere Straßen' (empty streets).
Am Sonntagmorgen sind die Straßen in der Innenstadt oft wie leer gefegt.
On Sunday mornings, the streets in the city center often look completely deserted.
When 'leer' (blank/empty) describes an expressionless facial expression, it is almost always used together with words like 'Blick' (look/gaze), 'Augen' (eyes), or 'Gesicht' (face).
Sie gab mir nur einen leeren Blick und sagte nichts.
She just gave me a blank look and said nothing.
In colloquial language, the word 'alle' (dead/used up) is often used instead of 'leer' when talking about rechargeable batteries or batteries. Both formulations are correct and common.
Mein Akku ist schon wieder alle, ich muss das Handy laden.
My battery is dead again; I have to charge the phone.
To express a feeling of inner emptiness, 'leer' (empty) is often combined with the reflexive verb 'sich fühlen' (to feel). The construction is 'sich leer fühlen' (to feel empty).
Nach dem Ende des Projekts fühlte er sich plötzlich ganz leer.
After the end of the project, he suddenly felt completely empty.
all
'all' and 'leer' can both mean that there is nothing left. 'leer' is the normal word when a container has no contents or a battery has no charge left. 'all' is used colloquially for things that have been used up, for example milk, bread, or money. Learners may confuse the words because both can fit everyday situations. 'Die Flasche ist leer' (the bottle is empty) describes the state. 'Die Milch ist alle' (the milk is all gone) suggests more: it has been used up; we have no more.

Heute ist der Akku meines Handys leer, deshalb kann ich nicht anrufen.
My phone battery is dead today, so I can't call.
Ist der Kaffee schon alle, oder kann ich noch eine Tasse nehmen?
Is the coffee already all gone, or can I still have a cup?