Preposition "bei" and "in" to express "in/at a place"

Question

In case of "WO", when do we use "bei + dativ" and/or "in + dativ"? What is the difference?

Answer 1

Question/Frage:

"Wo bist du?"

"Where are you?"

Answer/Antwort:

"Ich bin bei Peter." (I'm at Peter's (place)).

Case used for persons/people mostly.

"Ich bin in der Bar." (I'm in/at the bar).

Case mostly used for places.

That should pretty much sum up what you are asking, I guess.

Answer 2

in + Dativ

^{(note, that »in + dem« becomes »im«)}
»In« is used, if something is located ...

• inside a building

  Ich bin im Haus. (= Ich bin in dem Haus.)
  I'm in the house.

  Lisa ist in der Schule.
  Lisa is in school.

• in a country or continent

  Ernst ist gerade in Japan.
  Ernst is currently in Japan.

  Kenya liegt in Afrika.
  Kenya is located in Africa.

• in a region

  Ich mache Urlaub in den Alpen.
  I'm on holiday in the Alps.

  Karl lebt in der Stadt.
  Karl lives in the city.

• in a street, alley, ...

  Ich bin jetzt in der Grillparzerstraße.
  I am now in Grillparzerstrasse.

  Erika wohnt in der Maigasse.
  Erika lives in Maigasse.

---

bei + Dativ

^{(note, that »bei + dem« becomes »beim«)}
»In« is used, if ...

• a location is located near a city

  Monika arbeitet in Baden bei Wien.
  Monika works in Baden near Vienna.

  Helmut kauft Tickets für den Freizeitpark bei Leipzig.
  Helmut buys tickets for the Freizeitpark near Leipzig.

• something is located near something else

  Ich meine die Bank bei den drei Eichen.
  I mean the bench at the three oaks.

  Kochlöffel finden Sie bei den Haushaltswaren.
  Cooking spoons can be found in the household goods.

• someone is located near another person

  Eugen ist gerade beim Chef. (= Eugen ist gerade bei dem Chef.)
  Eugen is currently at the boss.

  Ich war gestern bei Christa.
  I visited Christa yesterday.

• someone works at a company

  Lukas arbeitet bei der Post.
  Lukas works at the post office.

  Maria arbeitet bei einer Bank.
  Maria works at a Bank.

Answer 3

"In" refers to being inside "places." Ich bin im Restaurant. I am in the Restaurant.

"Bei" refers to being part of, or a member of, an institution or a group. A better translation than "in" is "with." Ich bin bei der Uni. I am with the University (e.g. as a professor). On the other hand,"Ich bin in der Uni" would mean, I am inside the University (building).

A tricky phrase is "Ich bin bei Tom." In German, that means, "I am with Tom" (probably at Tom's house.)

But an English speaker might say, "I am at/in Tom's" (house).